부산대학교 도서관

Bile acids are synthesized de novoin the liver from cholesterol and conjugated to glycine or taurine via a complex series of reactions involving multiple organelles. Bile acids secreted into the small intestine are efficiently reabsorbed and reutilized. Activation by thioesterification to CoA is required at two points in bile acid metabolism. First, 3α,7α,12α-trihydroxy-5β-cholestanoic acid, the 27-carbon precursor of cholic acid, must be activated to its CoA derivative before side chain cleavage via peroxisomal β-oxidation. Second, reutilization of cholate and other C24bile acids requires reactivation prior to re-conjugation. We reported previously that homolog 2 of very long-chain acyl-CoA synthetase (VLCS) can activate cholate (Steinberg, S. J., Mihalik, S. J., Kim, D. G., Cuebas, D. A., and Watkins, P. A. (2000)J. Biol. Chem.275, 15605–15608). We now show that this enzyme also activates chenodeoxycholate, the secondary bile acids deoxycholate and lithocholate, and 3α,7α,12α-trihydroxy-5β-cholestanoic acid. In contrast, VLCS activated 3α,7α,12α-trihydroxy-5β-cholestanoate, but did not utilize any of the C24bile acids as substrates. We hypothesize that the primary function of homolog 2 is in the reactivation and recycling of C24bile acids, whereas VLCS participates in the de novosynthesis pathway. Results ofin situhybridization, topographic orientation, and inhibition studies are consistent with the proposed roles of these enzymes in bile acid metabolism.