Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    The anti-browning agent sulfite inactivates Agaricus bisporus tyrosinase through covalent modification of the copper-B site
    Kuijpers, T.F.M. ; Gruppen, H. ; Sforza, S. ; Berkel, W.J.H. van; Vincken, J.P. - \ 2013
    FEBS Journal 280 (2013)23. - ISSN 1742-464X - p. 6184 - 6195.
    glutathione conjugate formation - crystal-structure - mushroom tyrosinase - polyphenol oxidase - chlorogenic acid - plant - inhibition - metabolism - thioether - sequence
    Sulfite salts are widely used as antibrowning agents in food processing. Nevertheless, the exact mechanism by which sulfite prevents enzymatic browning has remained unknown. Here, we show that sodium hydrogen sulfite (NaHSO3 ) irreversibly blocks the active site of tyrosinase from the edible mushroom Agaricus bisporus, and that the competitive inhibitors tropolone and kojic acid protect the enzyme from NaHSO3 inactivation. LC-MS analysis of pepsin digests of NaHSO3 -treated tyrosinase revealed two peptides showing a neutral loss corresponding to the mass of SO3 upon MS(2) fragmentation. These peptides were found to be homologous peptides containing two of the three histidine residues that form the copper-B-binding site of mushroom tyrosinase isoform PPO3 and mushroom tyrosinase isoform PPO4, which were both present in the tyrosinase preparation used. Peptides showing this neutral loss behavior were not found in the untreated control. Comparison of the effects of NaHSO3 on apo-tyrosinase and holo-tyrosinase indicated that inactivation is facilitated by the active site copper ions. These data provide compelling evidence that inactivation of mushroom tyrosinase by NaHSO3 occurs through covalent modification of a single amino-acid residue, probably via addition of HSO3 (-) to one of the copper-coordinating histidines in the copper-B site of the enzyme
    Main Phenolic Compounds of the Melanin Biosynthesis Pathway in Bruising-Tolerant and Bruising-Sensitive Button Mushroom (Agaricus bisporus) Strains
    Weijn, A. ; Berg-Somhorst, B.P.M. van de; Slootweg, J.C. ; Vincken, J.P. ; Gruppen, H. ; Wichers, H.J. ; Mes, J.J. - \ 2013
    Journal of Agricultural and Food Chemistry 61 (2013)34. - ISSN 0021-8561 - p. 8224 - 8231.
    polyphenol oxidase - fungal melanins - amino-acids
    Browning is one of the most common postharvest changes in button mushrooms, which often results in economic losses. Phenolic compounds, which are associated with browning, were extracted from the nonbruised and bruised skin tissue of various button mushrooms with a sulfite-containing solution and analyzed with UHPLC-PDA-MS. In total, 34 phenolic compounds were detected. Only small differences in the total phenolic content between bruising-tolerant and -sensitive strains were observed. The contents of ¿-l-glutaminyl-4-hydroxybenzene (GHB) and ¿-l-glutaminyl-3,4-dihydroxybenzene (GDHB) correlated with bruising sensitivity; for example, R2 values of 0.85 and 0.98 were found for nonbruised brown strains, respectively. In nonbruised skin tissue of the strains with brown caps, the GHB and GDHB contents in sensitive strains were on average 20 and 15 times higher, respectively, than in tolerant strains. GHB and GDHB likely participate in the formation of brown GHB–melanin, which seemed to be the predominant pathway in bruising-related discoloration of button mushrooms.
    Analysis of genetically modified red-fleshed apples reveals effects on growth and consumer attributes
    Espley, R.V. ; Bovy, A.G. ; Bava, C. ; Jaeger, S.R. ; Tomes, S. ; Norling, C. ; Crawford, J. ; Rowan, D. ; McGhie, T.K. ; Brendolise, C. ; Putterill, J. ; Schouten, H.J. ; Hellens, R.P. ; Allan, A.C. - \ 2013
    Plant Biotechnology Journal 11 (2013)4. - ISSN 1467-7644 - p. 408 - 419.
    myb transcription factor - polyphenol oxidase - tomato fruit - factor gene - anthocyanins - leaves - plants - biosynthesis - expression - protein
    Consumers of whole foods, such as fruits, demand consistent high quality and seek varieties with enhanced health properties, convenience or novel taste. We have raised the polyphenolic content of apple by genetic engineering of the anthocyanin pathway using the apple transcription factor MYB10. These apples have very high concentrations of foliar, flower and fruit anthocyanins, especially in the fruit peel. Independent lines were examined for impacts on tree growth, photosynthesis and fruit characteristics. Fruit were analysed for changes in metabolite and transcript levels. Fruit were also used in taste trials to study the consumer perception of such a novel apple. No negative taste attributes were associated with the elevated anthocyanins. Modification with this one gene provides near isogenic material and allows us to examine the effects on an established cultivar, with a view to enhancing consumer appeal independently of other fruit qualities.
    Melanin biosynthesis pathway in Agaricus bisporus mushrooms
    Weijn, A. ; Bastiaan-Net, S. ; Wichers, H.J. ; Mes, J.J. - \ 2013
    Fungal Genetics and Biology 55 (2013). - ISSN 1087-1845 - p. 42 - 53.
    quantitative trait locus - lecanicillium-fungicola - polyphenol oxidase - tyrosinase - expression - resistance - cloning - genes - metabolism
    With the full genome sequence of Agaricus bisporus available, it was possible to investigate the genes involved in the melanin biosynthesis pathway of button mushrooms. Based on different BLAST and alignments, genes were identified in the genome which are postulated to be involved in this pathway. Seven housekeeping genes were tested of which 18S rRNA was the only housekeeping gene that was stably expressed in various tissues of different developmental stages. Gene expression was determined for most gene homologs (26 genes) involved in the melanin pathway. Of the analysed genes, those encoding polyphenol oxidase (PPO), the PPO co-factor L-chain (unique for Agaricus bisporus), and a putative transcription factor (photoregulator B) were among the highest expressed in skin tissue. An in depth look was taken at the clustering of several PPO genes and the PPO co-factor gene on chromosome 5, which showed that almost 25% of the protein encoding genes in this cluster have a conserved NACHT and WD40 domain or a P-loop nucleoside triphosphate hydrolase. This article will be the start for an in depth study of the melanin pathway and the role in quality losses of this economically important product.
    Inhibition of Enzymatic Browning of Chlorogenic Acid by Sulfur-Containing Compounds
    Kuijpers, T.F.M. ; Narvaez Cuenca, C.E. ; Vincken, J.P. ; Verloop, J.W. ; Berkel, W.J.H. van; Gruppen, H. - \ 2012
    Journal of Agricultural and Food Chemistry 60 (2012)13. - ISSN 0021-8561 - p. 3507 - 3514.
    performance liquid-chromatography - polyphenol oxidase - ascorbic-acid - mass-spectrometry - addition-products - apple juice - lc-msn - tyrosinase - oxidation - cysteine
    The antibrowning activity of sodium hydrogen sulfite (NaHSO3) was compared to that of other sulfur-containing compounds. Inhibition of enzymatic browning was investigated using a model browning system consisting of mushroom tyrosinase and chlorogenic acid (5-CQA). Development of brown color (spectral analysis), oxygen consumption, and reaction product formation (RP-UHPLC–PDA–MS) were monitored in time. It was found that the compounds showing antibrowning activity either prevented browning by forming colorless addition products with o-quinones of 5-CQA (NaHSO3, cysteine, and glutathione) or inhibiting the enzymatic activity of tyrosinase (NaHSO3 and dithiothreitol). NaHSO3 was different from the other sulfur-containing compounds investigated, because it showed a dual inhibitory effect on browning. Initial browning was prevented by trapping the o-quinones formed in colorless addition products (sulfochlorogenic acid), while at the same time, tyrosinase activity was inhibited in a time-dependent way, as shown by pre-incubation experiments of tyrosinase with NaHSO3. Furthermore, it was demonstrated that sulfochlorogenic and cysteinylchlorogenic acids were not inhibitors of mushroom tyrosinase.
    Crystal Structure of Agaricus bisporus Mushroom Tyrosinase: Identity of the Tetramer Subunits and Interaction with Tropolone
    Ismaya, W.T. ; Rozeboom, H.J. ; Weijn, A. ; Mes, J.J. ; Fusetti, F. ; Wichers, H.J. ; Dijkstra, B.W. - \ 2011
    Biochemistry 50 (2011)24. - ISSN 0006-2960 - p. 5477 - 5486.
    polyphenol oxidase - diffraction data - multiple forms - protein - mechanism - sequence - inhibition - refinement - plant - activation
    Tyrosinase catalyzes the conversion of phenolic compounds into their quinone derivatives, which are precursors for the formation of melanin, a ubiquitous pigment in living organisms. Because of its importance for browning reactions in the food industry, the tyrosinase from the mushroom Agaricus bisporus has been investigated in depth. In previous studies the tyrosinase enzyme complex was shown to be a H(2)L(2) tetramer, but no clues were obtained of the identities of the subunits, their mode of association, and the 3D structure of the complex. Here we unravel this tetramer at the molecular level. Its 2.3 Å resolution crystal structure is the first structure of the full fungal tyrosinase complex. The complex comprises two H subunits of ~392 residues and two L subunits of ~150 residues. The H subunit originates from the ppo3 gene and has a fold similar to other tyrosinases, but it is ~100 residues larger. The L subunit appeared to be the product of orf239342 and has a lectin-like fold. The H subunit contains a binuclear copper-binding site in the deoxy-state, in which three histidine residues coordinate each copper ion. The side chains of these histidines have their orientation fixed by hydrogen bonds or, in the case of His85, by a thioether bridge with the side chain of Cys83. The specific tyrosinase inhibitor tropolone forms a pre-Michaelis complex with the enzyme. It binds near the binuclear copper site without directly coordinating the copper ions. The function of the ORF239342 subunits is not known. Carbohydrate binding sites identified in other lectins are not conserved in ORF239342, and the subunits are over 25 Å away from the active site, making a role in activity unlikely. The structures explain how calcium ions stabilize the tetrameric state of the enzyme
    New Insights into an Ancient Antibrowning Agent: Formation of Sulfophenolics in Sodium Hydrogen Sulfite-Treated Potato Extracts
    Narvaez Cuenca, C.E. ; Kuijpers, T.F.M. ; Vincken, J.P. ; Waard, P. de; Gruppen, H. - \ 2011
    Journal of Agricultural and Food Chemistry 59 (2011)18. - ISSN 0021-8561 - p. 10247 - 10255.
    tandem mass-spectrometry - chlorogenic acid - polyphenol oxidase - ascorbic-acid - quercetin - identification - inhibition - phenolics - oxidation - cysteine
    The effect of sodium hydrogen sulfite (S), used as antibrowning agent, on the phenolic profile of potato extracts was investigated. This extract was compared to one obtained in the presence of ascorbic acid (A). In the presence of A, two major compounds were obtained, 5-O-caffeoylquinic acid (5-CQA) and 4-O-caffeoyl quinic acid. With S, their 2'-sulfo-adducts were found instead, the structures of which were confirmed by nuclear magnetic resonance spectroscopy and mass spectrometry. Also, for minor caffeoyl derivatives and quercetin glycosides, the corresponding sulfo-adducts were observed. Feruloyl and sinapoyl derivatives were not chemically affected by the presence of S. Polyphenol oxidase (PPO) was thought to be responsible for the formation of the sulfo-adducts. This was confirmed by preparing 2'-sulfo-5-O-caffeoyl quinic acid in a model system using 5-CQA, sodium hydrogen sulfite, and PPO. This sulfo-adduct exhibited a small bathochromic shift (¿max 329 nm) as compared to 5-CQA (¿max 325 nm) and a strong hypochromic shift with an extinction coefficient of 9357 ± 395 M–1 cm–1 as compared to 18494 ± 196 M–1 cm–1, respectively. The results suggest that whenever S is used as an antibrowning agent, the O-quinone formed with PPO reacts with S to produce sulfo-O-diphenol, which does not participate in browning reactions.
    Crystallization and preliminary X-ray crystallographic analysis of tyrosinase from the mushroom Agaricus bisporus
    Ismaya, W.T. ; Rozeboom, H.J. ; Schurink, M. ; Boeriu, C.G. ; Wichers, H.J. ; Dijkstra, B.W. - \ 2011
    Acta Crystallographica Section F. Structural Biology and Crystallization Communications 67 (2011)5. - ISSN 1744-3091 - p. 575 - 578.
    diphenolase activities - polyphenol oxidase - monophenolase - expression - mechanism
    Tyrosinase catalyzes the conversion of tyrosine to dihydroxyphenylalanine quinone, which is the main precursor for the biosynthesis of melanin. The enzyme from Agaricus bisporus, the common button mushroom, was purified and crystallized in two different space groups. Crystals belonging to space group P21 (unit-cell parameters a = 104.2, b = 105.0, c = 119.1 Å, ß = 110.6°, four molecules per asymmetric unit) diffracted to 3.0 Å resolution. Crystals belonging to space group P21212 (unit-cell parameters a = 104.0, b = 104.5, c = 108.4 Å, two molecules per asymmetric unit) diffracted to 2.6 Å resolution. It was essential to include 5 mM HoCl3 in all crystallization conditions in order to obtain well diffracting crystals.
    Hot water treatments delay cold-induced banana peel blackening
    Promyou, S. ; Ketsa, S. ; Doorn, W.G. van - \ 2008
    Postharvest Biology and Technology 48 (2008)1. - ISSN 0925-5214 - p. 132 - 138.
    polyphenol oxidase - growth - leaves
    Banana fruit of cv. Gros Michel (Musa acuminata, AAA Group, locally called cv. Hom Thong) and cv. Namwa (Musa x paradisiaca, ABB Group) were immersed for 5, 10 and 15 min in water at 42 degrees C, or in water at 25 degrees C (control), and were then stored at 4 degrees C. Hot water treatment for 15 min delayed peel blackening during cold storage by about 4 days in cv. Gros Michel and by 2 days in cv. Namwa. In both cultivars the delay of blackening was correlated with an increase in the ratio of unsaturated to saturated fatty acids. Hot water treatment in cv. Gros Michel but not cv. Namwa was correlated with lower lipoxygenase (LOX) activity and lower levels of thiobarbitutic acid-reactive compounds. The results suggest that the rapid peel blackening of cv. Gros Michel is related to detectable membrane degradation, whereas the membrane-associated changes might be below the detection limit in the slower blackening cv. Namwa. The delay of peel blackening in cv. Gros Michel was associated with reduced expression of a catechol oxidase gene, which might partially explain the lower catechol oxidase activity after hot water treatment. The hot water treatment also increased the abundance of a Hsp70 transcript. The changes in gene expression found in cv. Gros Michel were not observed in cv. Namwa. Taken together the delay of blackening by hot water treatment in cv. Namwa was only correlated with a change in the ratio of unsaturated to saturated fatty acids, whereas that in cv. Gros Michel was additionally correlated with lower LOX activity, lower mRNA abundance of a gene encoding a catechol oxidase and lower catechol oxidase activity.
    Covalent interactions between amino acid side chains and oxidation products of caffeoylquinic acid (chlorogenic acid)
    Prigent, S.V.E. ; Voragen, A.G.J. ; Li, F. ; Visser, A.J.W.G. ; Koningsveld, G.A. van; Gruppen, H. - \ 2008
    Journal of the Science of Food and Agriculture 88 (2008)10. - ISSN 0022-5142 - p. 1748 - 1754.
    caffeic acid - polyphenol oxidase - plant phenols - proteins - model - inhibitor - compound - quinone - esters
    BACKGROUND: Physicochemical properties and digestibility of proteins can be modified by covalent interactions with oxidized phenolic compounds, i.e., quinones. In order to control these interactions in food products, the covalent interactions between quinones from caffeoylquinic acid (CQA) and amino acid side chains were studied with mass spectrometry using N-terminally protected amino acids. RESULTS: The addition of two molecules of CQA, presumably in the form of a pre-formed dimer, was observed for lysine, tyrosine, histidine and tryptophan. A monomer of CQA seemed to be able to react with histidine and tryptophan, whereas no interaction with a CQA monomer was observed for lysine and tyrosine. Serine and threonine showed no covalent interactions with CQA. Cross-linking between CQA and the side chains of two molecules of lysine is likely to occur also in proteins. The results show that protein cross-linking may also be expected to occur via two tyrosine residues in the absence of other phenolic substrates. The side chains of lysine and tyrosine are more reactive than that of histidine and tryptophan. CONCLUSIONS: These results show that covalent protein modification by oxidized phenolics occurs preferentially via an initial dimerization and encompasses not only lysine and cysteine residues.
    Unravelling enzymatic discoloration in potato through a combined approach of candidate genes, QTL, and expression analysis
    Werij, J.S. ; Kloosterman, B.A. ; Celis-Gamboa, C. ; Vos, C.H. de; America, A.H.P. ; Visser, R.G.F. ; Bachem, C.W.B. - \ 2007
    Theoretical and Applied Genetics 115 (2007)2. - ISSN 0040-5752 - p. 245 - 252.
    polyphenol oxidase - solanum-tuberosum - linkage maps - tomato - tyrosine - family - set
    Enzymatic discoloration (ED) of potato tubers was investigated in an attempt to unravel the underlying genetic factors. Both enzyme and substrate concentration have been reported to influence the degree of discoloration and as such this trait can be regarded as polygenic. The diploid mapping population C x E, consisting of 249 individuals, was assayed for the degree of ED and levels of chlorogenic acid and tyrosine. Using this data, Quantitative Trait Locus (QTL) analysis was performed. Three QTLs for ED have been found on parental chromosomes C3, C8, E1, and E8. For chlorogenic acid a QTL has been identified on C2 and for tyrosine levels, a QTL has been detected on C8. None of the QTLs overlap, indicating the absence of genetic correlations between these components underlying ED, in contrast to earlier reports in literature. An obvious candidate gene for the QTL for ED on Chromosome 8 is polyphenol oxidase (PPO), which was previously mapped on chromosome 8. With gene-specific primers for PPO gene POT32 a CAPS marker was developed. Three different alleles (POT32-1, -2, and -3) could be discriminated. The segregating POT32 alleles were used to map the POT32 CAPS marker and QTL analysis was redone, showing that POT32 coincides with the QTL peak. A clear correlation between allele combinations and degree of discoloration was observed. In addition, analysis of POT32 gene expression in a subset of genotypes indicated a correlation between the level of gene expression and allele composition. On average, genotypes having two copies of allele 1 had both the highest degree of discoloration as well as the highest level of POT32 gene expression.
    Covalent interactions between proteins and oxidation products of caffeoylquinic acid (chlorogenic acid)
    Prigent, S.V.E. ; Voragen, A.G.J. ; Visser, A.J.W.G. ; Koningsveld, G.A. van; Gruppen, H. - \ 2007
    Journal of the Science of Food and Agriculture 87 (2007)13. - ISSN 0022-5142 - p. 2502 - 2510.
    bovine serum-albumin - physicochemical characterization - proteolytic digestion - polyphenol oxidase - model solutions - caffeic acid - derivatives - tyrosine - systems - peroxidase
    BACKGROUND: The interactions between phenolic compounds and proteins can modify protein properties important in the food industry. To understand the effects of these interactions, the covalent interactions between caffeoylquinic acid (chlorogenic acid, CQA) oxidised by polyphenol oxidase (PPO) at acidic pH 6 (pH 6) and -lactalbumin, lysozyme and bovine serum albumin (BSA) were compared with non-enzymatically induced covalent interactions at alkaline pH (pH 9). The effects of these modifications on protein properties were examined. RESULTS: Both ways of modification seemed to result in protein modification mainly via dimeric rather than monomeric CQA quinones. These modifications led to a decrease in the number of free primary amino groups of the proteins. Modification with CQA alone induced a low degree of protein dimerisation, which also occurred through the action of PPO alone. Modification drastically reduced the solubility of lysozyme over a broad pH range, whereas that of -lactalbumin was strongly reduced only at pH values close to its pI. The solubility of BSA was much less affected than that of the other proteins and only at acidic pH. CONCLUSION: These results indicate some similarities between modifications at pH 6 and 9 and that both modifications clearly change the functional properties of globular proteins.
    The chitin-binding Cladosporium fulvum effector protein Avr4 is a virulence factor
    Esse, H.P. van; Bolton, M.D. ; Stergiopoulos, I. ; Wit, P.J.G.M. de; Thomma, B.P.H.J. - \ 2007
    Molecular Plant-Microbe Interactions 20 (2007)9. - ISSN 0894-0282 - p. 1092 - 1101.
    pathogenesis-related proteins - plant antifungal proteins - transgenic tomato plants - avirulence gene avr9 - disease resistance - arabidopsis-thaliana - polyphenol oxidase - cf-4-mediated resistance - hypersensitive response - microbial pathogens
    The biotrophic fungal pathogen Cladosporium fulvum (syn. Passalora fulva) is the causal agent of tomato leaf mold. The Avr4 protein belongs to a set of effectors that is secreted by C. fulvum during infection and is thought to play a role in pathogen virulence. Previous studies have shown that Avr4 binds to chitin present in fungal cell walls and that, through this binding, Avr4 can protect these cell walls against hydrolysis by plant chitinases. In this study, we demonstrate that Avr4 expression in Arabidopsis results in increased virulence of several fungal pathogens with exposed chitin in their cell walls, whereas the virulence of a bacterium and an oomycete remained unaltered. Heterologous expression of Avr4 in tomato increased the virulence of Fusarium oxysporum f. sp. lycopersici. Through tomato GeneChip analyses, we demonstrate that Avr4 expression in tomato results in the induced expression of only a few genes. Finally, we demonstrate that silencing of the Avr4 gene in C. fulvum decreases its virulence on tomato. This is the first report on the intrinsic function of a fungal avirulence protein that has a counter-defensive activity required for full virulence of the pathogen.
    Biochemical characterization of the major sorghum grain peroxidase
    Dicko, M.H. ; Gruppen, H. ; Hilhorst, M.H. ; Voragen, A.G.J. ; Berkel, W.J.H. van - \ 2006
    FEBS Journal 273 (2006)10. - ISSN 1742-464X - p. 2293 - 2307.
    cationic peroxidases - polyphenol oxidase - covalent structure - phenolic-compounds - thermal-stability - hydrogen-peroxide - molecular-cloning - cross-linking - ferulic acid - gene family
    The major cationic peroxidase in sorghum grain (SPC4) , which is ubiquitously present in all sorghum varieties was purified to apparent homogeneity, and found to be a highly basic protein (pI 11). MS analysis showed that SPC4 consists of two glycoforms with molecular masses of 34227 and 35629 Da and it contains a type-b heme. Chemical deglycosylation allowed to estimate sugar contents of 3.0% and 6.7% (w/w) in glycoform I and II, respectively, and a mass of the apoprotein of 33 246 Da. High performance anion exchange chromatography allowed to determine the carbohydrate constituents of the polysaccharide chains. The N-terminal sequence of SPC4 is not blocked by pyroglutamate. MS analysis showed that six peptides, including the N-terminal sequence of SPC4 matched with the predicted tryptic peptides of gene indice TC102191 of sorghum chromosome 1, indicating that TC102191 codes for the N-terminal part of the sequence of SPC4, including a signal peptide of 31 amino acids. The N-terminal fragment of SPC4 (213 amino acids) has a high sequence identity with barley BP1 (85%), rice Prx23 (90%), wheat WSP1 (82%) and maize peroxidase (58%), indicative for a common ancestor. SPC4 is activated by calcium ions. Ca2+ binding increased the protein conformational stability by raising the melting temperature (Tm) from 67 to 82 °C. SPC4 catalyzed the oxidation of a wide range of aromatic substrates, being catalytically more efficient with hydroxycinnamates than with tyrosine derivatives. In spite of the conserved active sites, SPC4 differs from BP1 in being active with aromatic compounds above pH 5
    Effects of germination on the activities of amylases and phenolic enzymes in sorghum varieties grouped according to food end-use properties
    Dicko, M.H. ; Gruppen, H. ; Zouzouho, O.C. ; Traore, A.S. ; Berkel, W.J.H. van; Voragen, A.G.J. - \ 2006
    Journal of the Science of Food and Agriculture 86 (2006)6. - ISSN 0022-5142 - p. 953 - 963.
    phenylalanine ammonia-lyase - polyphenol oxidase - beta-amylase - cyanide contents - alpha-amylase - burkina-faso - peroxidase - cultivars - malt - viscosity
    Fifty sorghum varieties were screened to determine the effects of germination on levels of starch, -amylase, -amylase, phenylalanine ammonia lyase (PAL), peroxidase (POX) and polyphenol oxidase (PPO). Germination decreased starch content, with amylose being more degraded than amylopectin. In germinated grain, -amylase activity increased several-fold in all varieties, whereas -amylase activity did not increase uniformly and even decreased in some varieties. Activity of the key enzyme in phenolic biosynthesis, PAL, was detected in only half of the varieties before germination but in all of them after germination. PPO was not activated in germinated sorghum grains, whereas POX activity increased up to tenfold in some varieties. Zymography revealed that germination induced de novo synthesis of several POX isoenzymes, among which an anionic POX isoenzyme (pI 3.1) was ubiquitously present. Amylase and phenolic enzyme activities could be correlated with grain and plant agronomic characteristics. The use of sorghum varieties for local dishes such as tô, dolo, couscous and thin porridge could be correlated with amylase and phenolic enzyme activities and the contents of their substrates. The biochemical constituents determined are useful markers for selection of varieties for food utilisation with special emphasis on infant porridges.
    Impact of phenolic compounds and related enzymes in Sorghum varieties for resistance and susceptibility to biotic and abiotic stresses
    Dicko, M.H. ; Gruppen, H. ; Barro, C. ; Traore, A.S. ; Berkel, W.J.H. van; Voragen, A.G.J. - \ 2005
    Journal of Chemical Ecology 31 (2005)11. - ISSN 0098-0331 - p. 2671 - 2688.
    grain mold resistance - 3-deoxyanthocyanidin phytoalexins - polyphenol oxidase - burkina-faso - peroxidase - genotypes - apigeninidin - accumulation - mechanisms - sorghicola
    Contents of phenolic compounds and related enzymes before and after sorghum grain germination were compared between varieties either resistant or susceptible to biotic (sooty stripe, sorghum midge, leaf anthracnose, striga, and grain molds) and abiotic (lodging, drought resistance, and photoperiod sensitivity) stresses. Independent of grain germination, sorghum varieties resistant to biotic and abiotic stresses had on average higher contents of proanthocyanidins (PAs), 3-deoxyanthocyanidins (3-DAs), and flavan-4-ols than susceptible varieties. Results show that content of 3-DAs is a good marker for sorghum resistance to both biotic and abiotic stresses because it correlates with resistance to all stresses except for photoperiod sensitivity. The second good marker for stress resistance is content of PAs. Total phenolic compounds and the activities of related enzymes are not good markers for stress resistance in sorghum grains
    Senescent spotting of banana peel is inhibited by modified atmosphere packaging
    Choehom, R. ; Ketsa, S. ; Doorn, W.G. van - \ 2004
    Postharvest Biology and Technology 31 (2004)2.. - ISSN 0925-5214 - p. 167 - 175.
    phenylalanine ammonia-lyase - polyphenol oxidase - storage - biochemistry - physiology - tyrosinase - oxidation - tissue - oxygen - plants
    Banana fruit (Musa cavendishii [Musa acuminata] AA Group cv. Sucrier) were placed in trays and held at 29-30 degreesC. Covering the trays with 'Sun wrap' polyvinyl chloride film prevented the early senescent peel spotting, typical for this cultivar. Carbon dioxide and ethylene concentrations within the packages increased, but inclusion of carbon dioxide scrubbers or ethylene absorbents, which considerably affected gas composition, had no effect on spotting. Experiments with continuous low oxygen concentrations confirmed that the effect of the package was mainly due to low oxygen. Relative humidity was higher in the packages but this had no effect on spotting. The positive effect of modified atmosphere packaging on peel spotting was accompanied by reduced in vitro phenylalanine ammonia lyase (PAL) activity in the peel, and by an increase of in vitro polyphenol oxidase (PPO; catechol oxidase) activity. We conclude that senescent spotting of banana peel requires rather high oxygen levels. It is not known which reaction becomes limiting for spotting, at low oxygen levels. Whatever the mechanism, the increase of in vitro PPO activity apparently shows an increase in potentially active protein. (C) 2003 Elsevier B.V. All rights reserved.
    Wound-induced and bacteria-induced xylem blockage in roses, Astilbe and Viburnum
    Loubaud, M. ; Doorn, W.G. van - \ 2004
    Postharvest Biology and Technology 32 (2004)3. - ISSN 0925-5214 - p. 281 - 288.
    cut chrysanthemum flowers - polyphenol oxidase - cathechol oxidase - peroxidase - occlusion - tissue - stems
    We previously concluded that the xylem blockage that prevents water uptake into several cut flowers is mainly due to the presence of bacteria, whilst in chrysanthemum and Bouvardia we observed a xylem occlusion that was mainly due to a wound-reaction of the plant. We have further tested which of these two mechanisms was dominant in Astilbe,Viburnum and rose flowers. Astilbe x arendsii (cvs. Erica and Glut) flowers were stored dry in plastic bags (24 h at 5 degreesC, 100% RH) and placed in water at 20 degreesC without recutting the steins. The dry storage treatment considerably hastened a wounding-induced xylem occlusion in the stems. A 5 h pulse treatment with inhibitors of peroxidase (hydroquinone) and catechol oxidase (tropolone and 2,3-dihydroxynaphtalene), prior to dry storage, considerably delayed the xylem blockage. The 24 h dry storage treatment had no effect in rose (Rosa x hybrida cv. Red One), and Viburnum opulus (cv. Roseum). These flowers were therefore directly placed in water, with and without enzyme inhibitors. Except hydroquinone, all tested enzyme inhibitors reduced bacterial growth in the vase water. The latter chemicals could therefore not be used to distinguish between a plant-induced and a bacterial occlusion of the xylem. Hydroquinone had no effect on the time to wilting in roses, nor in Viburnum. It considerably delayed wilting in Astilbe flowers that were directly placed in water after harvest. It is concluded that the blockage in Astilbe is mainly due to the plant-induced xylem occlusion. The xylem occlusion in the tested rose and Viburnum cultivar was apparently not due to this mechanism. (C) 2004 Elsevier B.V. All rights reserved.
    Cloning, expression and characterisation of two tyrosinase cDNAs from Agaricus bisporus
    Wichers, H.J. ; Recourt, K. ; Hindriks, M. ; Ebbelaar, C.E.M. ; Biancone, G. ; Hoeberichts, F.A. ; Mooibroek, A. - \ 2003
    Applied Microbiology and Biotechnology 61 (2003)4. - ISSN 0175-7598 - p. 336 - 341.
    polyphenol oxidase - activation - isoform - harvest - plant - gene
    Using primers designed on the basis of sequence homologies in the copper-binding domains for a number of plant and fungal tyrosinases, two tyrosinase encoding cDNAs were cloned from an Agaricus bisporus U1 cDNA-library. The sequences AbPPO1 and AbPPO2 were, respectively, 1.9 and 1.8 kb in size and encoded proteins of approximately 64 kDa. The cDNAs represent different loci. Both AbPPO1 and AbPPO2 occur as single copies on the genomes of the U1 parental strains H39 and H97. The genomic size of AbPPO1 and AbPPO2 is minimally 2.3 and 2.2 kb, respectively. Alignment and phylogenetic analysis of 35 tyrosinase and polyphenol oxidase sequences of animal, plant, fungal, and bacterial origin indicated conserved copper-binding domains, and stronger conservation within genera than between them. The translation products of AbPPO1 and AbPPO2 possess putative N-glycosylation and phosphorylation sites and are recognised by antibodies directed against a 43-kDa tyrosinase. The observations are consistent with previously proposed maturation and activation models for plant and fungal tyrosinases.
    Xylem occlusion in Bouvardia flowers : evidence for a role of peroxidase and catechol oxidase
    Vaslier, N. ; Doorn, W.G. van - \ 2003
    Postharvest Biology and Technology 28 (2003)2. - ISSN 0925-5214 - p. 231 - 237.
    cut chrysanthemum flowers - polyphenol oxidase - tissue - water - cells - stems
    During vase life, Bouvardia flowers show rapid leaf wilting, especially if they are stored dry prior to placement in water. Wilting is due to a blockage in the basal stem end. We investigated the possible role of peroxidase and catechol oxidase in the blockage in cv. van Zijverden flowers, which were placed, for 5 h at 20 °C, in an aqueous solution containing enzyme inhibitors. Flowers were then stored dry in plastic bags (24 h at 5 °C, 100% RH) and placed in water at 20 °C without recutting the stems. Inhibitors of both peroxidase (hydroquinone, p-phenylene diamine, copper ions) and catechol oxidase (tropolone, 2,3-dihydroxynaphtalene) considerably delayed the time to leaf wilting. It is concluded that the blockage is apparently due to a wounding reaction and that it involves both peroxidase and catechol oxidase activity
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