The Journal of Biological Chemistry

The synthesis of 2-oxo-cis-4-hexenoic acid from DL-2amino-cis-4-hexenoic acid is described. The ~0x0 acid appears to exist at neutral pH largely in the dienolic form. Ultracentrifuged extracts of steroid-induced Pseudomonas iestosteroni rapidly converted 2-oxo-cis-4-hexenoic acid-lw to wo*. The same enzyme preparations, when supplemented with NAD and a NADPH-generating system, have been previously shown to convert A4-androstene-3, 17-dione4-r4C to r4C02 and to accumulate L-2-amino-cis-4-hexenoic acid-lJ*C and DL-alanine-l-14C in the presence of ethylenediaminetetraacetate. It has now been shown that, under similar conditions, 2-oxo-cis-4-hexenoic acid is efficiently converted to 2-amino-cis-4-hexenoic acid and alanine. The ~0x0 acid also undergoes stereospecific enzymatic hydration to 2-oxo-4-hydroxyhexanoic acid, which is lactonized in the presence of acid to give a product that has been identified as one of the optically active isomers of 2-0x0-4ethylbutyrolactone of unestablished configuration. These findings suggest that 2-oxo-cis-4-hexenoic acid is a key intermediate in the degradation of steroid ring A by microbial enzymes. The enzyme preparations also contain an enzyme which reduces the double bond of the (Y-0x0 acid but does not appear to be involved in the degradative pathway of the steroids.