Document Detail


Nonenzymatic acetolactate oxidation to diacetyl by flavin, nicotinamide and quinone coenzymes.
MedLine Citation:
PMID:  8541313     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Acetolactate nonenzymatically reduced flavins, quinones and nicotinamide coenzymes in a time-dependent manner at physiological pH and moderate temperature. In the presence of excess acetolactate, the reduction of FAD and NAD+ followed pseudo-first-order kinetics. The rate of reduction was proportional to the concentration of acetolactate, and the rate constants at 37 degrees C and pH 7.5 were 4.8 x 10(-2) M-1 s-1 and 7.4 x 10(-3) M-1 s-1 for FAD and NAD+, respectively. In contrast, ubiquinone reduction followed pseudo-zero-order kinetics in the presence of excess acetolactate. At 37 degrees C and pH 7.5, the rate of reduction was proportional to the acetolactate concentration, and the apparent rate constant was 8.3 x 10(-6) s-1. In contrast to FAD, the rate of reduction of ubiquinone was higher at low pH. The kinetics of ubiquinone reduction suggested that the rate-limiting step was acetolactate decarboxylation and formation of the enolate anion, whereas the rate of FAD reduction was governed by the second-order reaction of the enolate anion. Following the oxidation, acetolactate was converted to diacetyl. Reduced FAD formed by the reaction with acetolactate generated a low rate of O2 consumption during assays of the oxygenase activity of acetohydroxy acid synthase. The reaction of acetolactate with quinones may provide a mechanism for the nonenzymatic formation diacetyl in whole milk.
Authors:
H S Park; R Xing; W B Whitman
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Biochimica et biophysica acta     Volume:  1245     ISSN:  0006-3002     ISO Abbreviation:  Biochim. Biophys. Acta     Publication Date:  1995 Dec 
Date Detail:
Created Date:  1996-02-13     Completed Date:  1996-02-13     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0217513     Medline TA:  Biochim Biophys Acta     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  366-70     Citation Subset:  IM    
Affiliation:
Department of Microbiology, University of Georgia, Athens 30602-2605, USA.
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MeSH Terms
Descriptor/Qualifier:
Benzoquinones / metabolism*
Chromatography, Thin Layer
Diacetyl / metabolism*
Flavins / metabolism*
Lactates / metabolism*
Niacinamide / metabolism*
Oxidation-Reduction
Chemical
Reg. No./Substance:
0/Benzoquinones; 0/Flavins; 0/Lactates; 106-51-4/benzoquinone; 431-03-8/Diacetyl; 535-17-1/alpha-acetolactate; 98-92-0/Niacinamide

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