Kurosawa T, Sato M, Yoshimura T, Jiang L L, Hashimoto T, Tohma M
Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Japan.
Biol Pharm Bull. 1997 Mar;20(3):295-7. doi: 10.1248/bpb.20.295.
The absolute configuration of 3 alpha,7 alpha,12 alpha, 24-tetrahydroxy-5 beta-cholestan-26-oic acid CoA ester (V-CoA) produced by the incubation of (24E)-3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-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.
研究了将(24E)-3α,7α,12α-三羟基-5β-胆甾-24-烯-26-酸辅酶A酯（24E-THC-CoA）与D-3-羟酰基辅酶A脱水酶/D-3-羟酰基辅酶A脱氢酶（D-双功能蛋白）温育所产生的3α,7α,12α,24-四羟基-5β-胆甾烷-26-酸辅酶A酯（V-CoA）的绝对构型。当24E-THC-CoA与D-双功能蛋白温育时，观察到V-CoA的四种可能立体异构体中仅形成一种异构体（24R,25R-异构体），这表明水顺式加成到24E-THC-CoA的侧链双键上。当使用(24R,25R)-V-CoA作为底物时，也观察到D-双功能蛋白催化V-CoA的脱水反应。其他三种异构体（24R,25S-、24S,25R-和24S,25S-异构体）不能被D-双功能蛋白脱水。这些结果表明，D-双功能蛋白在胆汁酸生物合成中立体特异性地催化水合和脱水步骤。
