A method for simultaneous determination of the two possible products of acetohydroxy acid synthase.

A method for the simultaneous assay of 2-acetolactate and 2-aceto-2-hydroxybutyrate formation catalyzed by acetohydroxy acid synthase in the presence of its substrates pyruvate and 2-ketobutyrate is described. The method, appropriate for the study of the physiologically and mechanistically significant competition between the two reactions, involves oxidative decarboxylation of the acetohydroxy acids to the corresponding 2,3-diketones, transfer of the volatile diketones to methanol, and gas chromatographic analysis with electron-capture detection. Oxidative decarboxylation by air requires catalytic activation, and addition of iron salts is crucial to the success of the method with purified enzymes.