Novel transformations of i-cholesterol and 6β-methoxy-i-cholesterol by Moraxella Sp.

Abstract

A soil microorganism was isolated by the enrichment culture technique using cholesterol as the sole source of carbon. The organism has been identified as belonging to the genus Moraxella. With this organism two novel biotransformations of sterols were observed viz. (1) isomerization of 3α,5α-cyclocholestan-6β-ol (i-cholesterol) to cholesterol. (2) demethylation of 6β-methoxy-3α,5α-cyclocholestane (6β-methoxy-i-cholesterol) to i-cholesterol with subsequent isomerization to cholesterol. The enzymes responsible for these transformations were shown to be inducible. The pH optimum of the partially purified i-cholesterol isomerase was found to be 8.4. The apparent K_m value for i-cholesterol was 1.43 μM. A plausible mechanism for the i-cholesterol isomerization has been discussed.