Nonenzymatic acetolactate oxidation to diacetyl by flavin, nicotinamide and quinone coenzymes
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 proportio...
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Published in | Biochimica et biophysica acta Vol. 1245; no. 3; pp. 366 - 370 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Netherlands
Elsevier B.V
14.12.1995
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Subjects | |
Online Access | Get full text |
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Summary: | 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°C and pH 7.5 were 4.8 · 10
−2 M
−1 s
−1 and 7.4 · 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°C and pH 7.5, the rate of reduction was proportional to the acetolactate concentration, and the apparent rate constant was 8.3 · 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 O
2 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. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0304-4165 0006-3002 1872-8006 |
DOI: | 10.1016/0304-4165(95)00103-4 |