Stereospecificity of vitamin K-epoxide reductase.
Vitamin K epoxide can occur as a pair of optical isomers due to the asymmetry of the oxirane ring substituents. The stereoselectivity of vitamin K-epoxide reductase for the oxirane ring configuration was determined by recovery of the partially resolved unreacted substrate following incubations of racemic vitamin K epoxide with rat liver microsomes. The substrate ws enriched for the (--)-enantiomer, but selectivity for the biologically relevant (+)-enantiomer was low. This result was confirmed by direct comparison of the rates of reaction for the racemic substrate and (+)-vitamin K epoxide. The selectivity of vitamin K-epoxide reductase for the cis- or trans-phytyl configuration of the vitamin K side chain was also low. These results suggest an enzyme-active site which is open toward the 2,3-positions and is able to bind the substrate in two opposite orientations with respect to the positions of the methyl and phytyl side chain substituents.[1]References
- Stereospecificity of vitamin K-epoxide reductase. Preusch, P.C., Suttie, J.W. J. Biol. Chem. (1983) [Pubmed]
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