Synthesis of delta 5,22-cholestadien-3 beta-ol from delta 5,7,22-cholestatrien-3 beta-ol by a liver enzyme.

The rat liver enzyme system, which catalyzes reduction of delta 5,7,24-cholestatrien-3 beta-ol to cholesterol (delta 5-cholesten-3 beta-ol), converted radiolabeled delta 5,7,22-cholestatrien-3 beta-ol to delta 5,22-cholestadien-3 beta-ol, but not to cholesterol. This enzyme system thus contains membrane-bound delta 7- and delta 24-reductase and no delta 22-reductase. Kinetic and competition studies showed that the enzyme system contains a single delta 5,7-sterol delta 7-reductase, which is not influenced by unsaturation at the delta 22-position of the sterol side chain. The identity of delta 5,22-cholestadienol was established by chromatographic, spectral and chemical analyses. Use of the enzyme system and readily available delta 5,7,22-cholestatrienol provides a facile procedure for specific production of delta 5,22-cholestadien-3 beta-ol in quantity.