| Popis: |
In addition to several other enzymes, the short-chain alcohol dehydrogenase superfamily includes a group of peroxisomal multifunctional enzymes involved in fatty acid and cholesterol side-chain β-oxidation. Mammalian peroxisomal multifunctional enzyme type 2 (perMFE-2) is a 2-enoyl-CoA hydratase-2/(R)-3-hydroxyacyl-CoA dehydrogenase. As has been shown previously, perMFE-2 hydrates (24E)-3α,7α,12α-trihydroxy-5β-cholest-24-enoyl-CoA to (24R, 25R)-3α,7α,12α,24ξ-tetrahydroxy-5β-cholestanoyl-CoA, which has been characterized as a physiological intermediate in cholic acid synthesis. Out of four possible stereoisomers of 3α,7α,12α,24ξ-tetrahydroxy-5β-cholestanoyl-CoA, the mammalian perMFE-2 dehydrogenates only the (24R,25R)-isomer. The yeast peroxisomal multifunctional enzyme (MFE) was first described as 2-enoyl-CoA hydratase-2/(R)-3-hydroxyacyl-CoA dehydrogenase. To investigate the stereospecificity of yeast peroxisomal MFE, the two dehydrogenase domains of C. tropicalis MFE were expressed in E. coli as a 65 kDa recombinant protein. This protein catalyzes the dehydrogenation of straight-chain (R)-3-hydroxyacyl-CoAs, but it is devoid of (S)-3-hydroxyacyl-CoA dehydrogenase and 2-enoyl-CoA hydratase activities. The protein dehydrogenates (24R,25R)- and (24R,25S)-isomers of 3α,7α, 12α,24ξ-tetrahydroxy-5β-cholestanoyl-CoA. Interestingly, the protein also shows 17β-estradiol dehydrogenase activity. As a monofunctional (R)-specific 3-hydroxyacyl-CoA dehydrogenase is currently unavailable, this recombinant enzyme can be used to study the stereochemistry of bile acid synthesis. —Qin, Y-M., M. H. Poutanen, and D. K. Novikov. Substrate specificities of peroxisomal members of short-chain alcohol dehydrogenase superfamily: expression and characterization of dehydrogenase part of Candida tropicalis multifunctional enzyme. |
