Studies on the Microbiological Degradation of Steroid Ring A

Abstract

The synthesis of 2-oxo-cis-4-hexenoic acid from DL-2-amino-cis-4-hexenoic acid is described. The α-oxo acid appears to exist at neutral pH largely in the dienolic form. Ultracentrifuged extracts of steroid-induced Pseudomonas testosteroni rapidly converted 2-oxo-cis-4-hexenoic acid-1-14C to 14CO2. The same enzyme preparations, when supplemented with NAD and a NADPH-generating system, have been previously shown to convert Δ4-androstene-3,17-dione-4-14C to 14CO2 and to accumulate L-2-amino-cis-4-hexenoic acid-1-14C and DL-alanine-1-14C in the presence of ethylenediaminetetraacetate. It has now been shown that, under similar conditions, 2-oxo-amino-cis-4-hexenoic acid is efficiently converted to 2-amino-cis-4-hexenoic acid and alanine. The α-oxo 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-oxo-4-ethylbutyrolactone 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 α-oxo acid but does not appear to be involved in the degradative pathway of the steroids.