DISCOVERY OF A NEW MECHANISM OF 2,3-BUTANEDIOL STEREOISOMER FORMATIONIN BACILLUS-CEREUS YUF-4

A mechanism of 2,3-butanediol (ED) stereoisomer formation was examined with respect to the ED cycle. The enzymes acetylacetoin synthase, ace tylacetoin reductase (AACR), and acetylbutanediol hydrolase (ABDH), wh ich are part of the ED cycle, were found to be present in the cell-fre e extract of the bacterial strain Bacillus cereus YUF-4. Two kinds of acetylbutanediol (ABD) stereoisomers were produced in the reduction of acetylacetoin (AAC) by AACR, which were identified as having 3R,4R an d 3S,4R configurations by NMR spectroscopy and an enzymic method. The two ABD formations were found to be catalyzed independently by two res pective enzymes: the former was catalyzed by a NADPH-dependent AACR (3 R,4R-ABD forming) and the latter by a NADH-dependent AACR (3S,4R-ABD f orming). The 3R,4R-ABD was converted into R,R-BD and the 3S,4R-ABD int o R,S-BD by intracellular ABDH. These findings demonstrated the existe nce of a new ED isomer formation mechanism derived from the ED cycle.