Cholic acid biosynthesis: conversion of 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol into 5beta-cholestane-3alpha,7alpha, 12alpha,24beta,25-pentol by human and rat liver microsomes.
This paper describes the conversion of 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol into 5beta-cholestane-3alpha,7alpha,12alpha,24beta,25-pentol by liver microsomes. A sensitive radioactive assay for measuring the formation of 5beta-cholestane-3alpha,7alpha,12alpha,24beta,25-pentol was developed. Optimal assay conditions for human and rat microsomal systems were established. A higher 24beta-hydroxylation activity was detected in rat than in human liver under the conditions employed. The hydroxylation of 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol by the rat liver microsomal fraction fortified with NADPH was stimulated about two-fold by administration of phenobarbital. Phenobarbital treatment also stimulated hydroxylations at C-23, C-24alpha, and C-26. Carbon monoxide markedly inhibited all side-chain hydroxylations. In contrast, side-chain hydroxylase activities were not affected in animals deprived of food for 48 hr. These results are consistent with a previously postulated cholic acid biosynthetic pathway involving 5beta-cholestane-3alpha,7alpha,12alpha,24beta,25-pentol as a key intermediate in man and in the rat.
D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology; D002793:Cholic Acids / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D013045:Species Specificity; D013250:Steroid Hydroxylases / Q000378:metabolism; D013261:Sterols / Q000378:metabolism*
D002793:Cholic Acids; D013261:Sterols; D002248:Carbon Monoxide; D013250:Steroid Hydroxylases; D010634:Phenobarbital