Document Detail

Diphenol activation of the monophenolase and diphenolase activities of field bean (Dolichos lablab) polyphenol oxidase.
MedLine Citation:
PMID:  11879044     Owner:  NLM     Status:  MEDLINE    
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.
Lalitha R Gowda; Beena Paul
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of agricultural and food chemistry     Volume:  50     ISSN:  0021-8561     ISO Abbreviation:  J. Agric. Food Chem.     Publication Date:  2002 Mar 
Date Detail:
Created Date:  2002-03-06     Completed Date:  2002-04-23     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0374755     Medline TA:  J Agric Food Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1608-14     Citation Subset:  IM    
Department of Protein Chemistry and Technology, Central Food Technological Research Institute, Mysore 570013, India.
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MeSH Terms
Benzoquinones / metabolism
Caffeic Acids / metabolism,  pharmacology
Catechin / metabolism
Catechol Oxidase / metabolism*
Catechols / pharmacology
Coumaric Acids / metabolism
Enzyme Activation / drug effects
Fabaceae / enzymology*
Oxygen Consumption
Phenols / pharmacology*
Substrate Specificity
Tyrosine / metabolism
Reg. No./Substance:
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 Oxidase

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