THIOLASE INVOLVED IN BILE-ACID FORMATION

The formation of cholic acid and chenodeoxycholic acid through cleavag e of the side chains of CoA esters of 3 alpha,7 alpha,12 alpha-trihydr oxy-B beta-cholestan-26-oic acid and 3 alpha,7 alpha-dihydroxy-5 beta- cholestan-26-oic acid is believed to occur in peroxisomes. Recently, w e found a new peroxisomal enzyme, D-3-hydroxyacyl-CoA dehydratase/D-3- hydroxyacyl-CoA dehydrogenase bifunctional protein, and suggested that this bifunctional protein is responsible for the conversion of 3 alph a,7 alpha,12 alpha-trihydroxy-5 beta-cholest-24-en-26-oyl-CoA and 3 al pha,7 alpha-dihydroxy-5 beta-cholest-24-en-26-oyl-CoA to their 24-ore- forms. In the present study, the products of this bifunctional protein reaction were analyzed by gas chromatography-mass spectrometry, and t he formation of 24-oxo-27-nor-cholestanes was confirmed. Previously, w e found a new thiolase in Caenorhabditis elegans, P-44, and suggested that P-44 and sterol carrier protein x, a peroxisomal protein, constit ute a second group of 3-oxoacyl-CoA thiolases. The production of choli c acid and chenodeoxycholic acid from the precursors on incubation wit h the bifunctional protein and sterol carrier protein x or P-44 was co nfirmed by gas chromatography.