Stereospecific formation of (24R,25R)-3α,7α,12α,24-tetrahydroxy-5β- cholestan-26-oic acid catalyzed with a peroxisomal bifunctional D-3- hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase

Abstract

The absolute configuration of 3α,7α,12α,24-tetrahydroxy-5β- cholestan-26-oic acid CoA ester (V-CoA) produced by the incubation of (24E)- 3α,7α,12α-trihydroxy-5β-cholest-24-en-26-oic acid CoA ester (24E-THC- CoA) with D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase (D-bifunctional protein) was investigated. When 24E-THC-CoA was incubated with D-bifunctional protein the formation of only one isomer (24R,25R- isomer) of four possible stereoisomers of V-CoA was observed, which suggested the cis-addition of water to a side chain double bond of 24E-THC-CoA. The dehydration reaction of V-CoA catalyzed by D-bifunctional protein was also observed when (24R,25R)-V-CoA was used as a substrate. The other three isomers (24R,25S-, 24S,25R- and 24S,25S-isomers) were not dehydrated with D- bifunctional protein. These results showed that D-bifunctional protein catalyzes stereospecifically the hydration and dehydration step in bile acid biosynthesis.