The chemical synthesis and biological oxidation of 7-alpha-hydroxy[26-14C]cholesterol, 7-dehydro[26-14C]cholesterol and 26-hydroxy[26-14C]cholesterol.

1. 26-Hydroxycholesterol was obtained by reducing the methyl ester of (+/-)-3beta-hydroxycholest-5-en-26-oic acid, which was synthesized from 25-oxonorcholesterol. 2. Methods for preparing 7alpha-hydroxycholesterol and 7-dehydrocholesterol were modified to allow the micro-scale preparation of these [(14)C]sterols from [26-(14)C]-cholesterol. 3. 26-Hydroxycholesterol was oxidized more readily than 7alpha-hydroxycholesterol, 7-dehydrocholesterol or cholesterol by mitochondrial preparations from livers of mice, rats, guinea pigs, common toads (Bufo vulgaris) and Caiman crocodylus. 4. (+/-)-3beta-Hydroxy[26-(14)C]cholest-5-en-26-oic acid was oxidized very rapidly to (14)CO(2) by mouse and guinea-pig mitochondria without evident discrimination between the two optical isomers. 5. An enzyme system that oxidizes 26-hydroxycholesterol to 3beta-hydroxycholest-5-en-26-oic acid was identified in the soluble extract of rat-liver mitochondria. This enzyme could use NADP in place of NAD but was not identical with liver alcohol dehydrogenase (EC 1.1.1.1). 6. [26-(14)C]Cholesteryl 3beta-sulphate was not oxidized by fortified mouse-liver preparations that oxidized [26-(14)C]cholesterol to (14)CO(2).