MECHANISM OF CHOLESTEROL REDUCTION TO COPROSTANOL BY EUBACTERIUM-COPROSTANOLIGENES ATCC-51222

The mechanism of reduction of cholesterol to coprostanol by Eubacteriu m coprostanoligenes ATCC 51222 was studied by incubating the bacterium with a mixture of alpha- and beta-isomers of [4-H-3,4-C-14]cholestero l. Coprostanol, isolated after incubation of [4-H-3,4-C-14]cholesterol in a growth medium under anaerobic conditions, retained 97% of the tr itium originally present in cholesterol. The majority of this tritium (64%), however was in the C-6 position in coprostanol, which showed th at the conversion of cholesterol into coprostanol by E. coprostanolige nes involved the intermediate formation of 4-cholesten-3-one followed by the reduction of the latter to coprostanol. In resting cell assays in which washed bacterial cells were incubated with micellar cholester ol in phosphate buffer at 37 degrees C, both 4-cholesten-3-one and cop rostanone were produced in addition to coprostanol. Furthermore, 5-cho lesten-3-one, 4-cholesten-3-one, and coprostanone were converted effic iently to coprostanol by E. coprostanoligenes. These results support t he hypothesis that the major pathway for reduction of cholesterol by E . coprostanoligenes involves the intermediate formation of 4-cholesten -3-one followed by reduction of the latter to coprostanol through copr ostanone as an intermediate.