Diacetyl oxidation by Streptococcus faecalis, a lipoic acid dependent reaction.

In the over-all reaction, one molecule of diacetyl is oxidized to two molecules of acetate, and another molecule of diacetyl is reduced to acetoin. The reaction was shown to require cocarboxylase (DPT).2 Subsequently, Schweet et al. (1951) expanded this finding and pointed out the similarity between the diacetyl reaction and pyruvic acid oxidation, with respect to the metabolism of the "active aldehyde" derived from the dicarbonyl split. Juni and Heym (1953), working with Aerobacter aerogenes, isolated two new compounds following diacetyl metabolism. One of them, diacetylmethylcarbinol, was formed by splitting diacetyl to form "active aldehyde", followed by a benzoin type of condensation of this aldehyde with another molecule of diacetyl. The other, acetylbutanediol, is a reduction product of diacetylmethylcarbinol. In the A. aerogenes system, the active aldehyde derived from diacetyl is not oxidized, but the condensation product, diacetylmethylcarbinol, undergoes further oxidation to acetate and diacetyl. Diacetyl-