| Diphenol activation of the monophenolase and diphenolase activities of field bean (Dolichos lablab) polyphenol oxidase. | |
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MedLine Citation:
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PMID: 11879044 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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This paper reports a study on the hydroxylation of ferulic acid and tyrosine by field bean (Dolichos lablab) polyphenol oxidase, a reaction that does not take place without the addition of catechol. A lag period similar to the characteristic lag of tyrosinase activity was observed, the length of which decreased with increasing catechol concentration and increased with increasing ferulic acid concentration. The activation constant K(a) of catechol for ferulic acid hydroxylation reaction was 5 mM. The kinetic parameters of field bean polyphenol oxidase toward ferulic acid and tyrosine were evaluated in the presence of catechol. 4-Methyl catechol, L-dihydroxyphenylalanine, pyrogallol, and 2,3,4-trihydroxybenzoic acid, substrates with high binding affinity to field bean polyphenol oxidase, could stimulate this hydroxylation reaction. In contrast, diphenols such as protocatechuic acid, gallic acid, chlorogenic acid, and caffeic acid, which were not substrates for the oxidation reaction, were unable to bring about this activation. It is most likely that only o-diphenols that are substrates for the diphenolase serve as cosubstrates by donating electrons at the active site for the monophenolase activity. The reaction mechanism for this activation is consistent with that proposed for tyrosinase (Sanchez-Ferrer, A.; Rodriguez-Lopez, J. N.; Garcia-Canovas, F.; Garcia-Carmona, F. Biochim. Biophys. Acta 1995, 1247, 1-11). The presence of o-diphenols, viz. catechol, L-dihydroxyphenylalanine, and 4-methyl catechol, is also necessary for the oxidation of the diphenols, caffeic acid, and catechin to their quinones by the field bean polyphenol oxidase. This oxidation reaction occurs immediately with no lag period and does not occur without the addition of diphenol. The kinetic parameters for caffeic acid (K(m) = 0.08 mM, V(max) = 32440 u/mg) in the presence of catechol and the activation constant K(a) of catechol (4.6 mM) for this reaction were enumerated. The absence of a lag period for this reaction indicates that the diphenol mechanism of diphenolase activation differs from the way in which the same o-diphenols activate the monophenolase activity. |
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Authors:
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Lalitha R Gowda; Beena Paul |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't |
Journal Detail:
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Title: Journal of agricultural and food chemistry Volume: 50 ISSN: 0021-8561 ISO Abbreviation: J. Agric. Food Chem. Publication Date: 2002 Mar |
Date Detail:
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Created Date: 2002-03-06 Completed Date: 2002-04-23 Revised Date: 2006-11-15 |
Medline Journal Info:
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Nlm Unique ID: 0374755 Medline TA: J Agric Food Chem Country: United States |
Other Details:
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Languages: eng Pagination: 1608-14 Citation Subset: IM |
Affiliation:
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Department of Protein Chemistry and Technology, Central Food Technological Research Institute, Mysore 570013, India. lrg@cscftri.ren.nic.in |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Benzoquinones
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metabolism Caffeic Acids / metabolism, pharmacology Catechin / metabolism Catechol Oxidase / metabolism* Catechols / pharmacology Coumaric Acids / metabolism Enzyme Activation / drug effects Fabaceae / enzymology* Hydroxylation Kinetics Oxidation-Reduction Oxygen Consumption Phenols / pharmacology* Spectrophotometry Substrate Specificity Tyrosine / metabolism |
| Chemical | |
Reg. No./Substance:
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0/Benzoquinones; 0/Caffeic Acids; 0/Catechols; 0/Coumaric Acids; 0/Phenols; 106-51-4/benzoquinone; 1135-24-6/ferulic acid; 154-23-4/Catechin; 331-39-5/caffeic acid; 55520-40-6/Tyrosine; EC 1.10.3.1/Catechol Oxidase |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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