title: The stereospecificity of the enzymic reduction of 21-dehydrocortisol by NADH.
abstract: (21R)-[21-3H]cortisol and (21S)-[21-3H]cortisol were synthesized by reduction of 21-dehydrocortisol by NADH in the presence of 21-hydroxysteroid dehydrogenase. The stereochemistry at carbon 21 was established after cleaving the side chain and oxidizing the resulting two epimers of tritiated glycolate with glycolate oxidase of known (2-pro-S) stereospecificity. From the distribution of radioactivity in the water and glyoxylate produced in this reaction, it was concluded that the reaction of 21-dehydrocortisol with (4S)-[4-3H]NADH catalyzed by 21-hydroxysteroid dehydrogenase results in a transfer of tritium from the 4S position of the nucleotide to form (21S)-[21-3H]cortisol, and that (21R)-[21-3H]cortisol resulted from the enzyme-catalyzed reduction of 21-dehydro[21-3H]cortisol with NADH. Nuclear magnetic resonance studies on both epimers at position 21 of [21-2H]cortisol and of [21-2H]cortisone prepared enzymically identify the transferring 21-pro-S hydrogen as the relatively downfield of the two 21-hydrogen atoms.
mesh_terms: D003903:Deuterium; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D013058:Mass Spectrometry; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D011239:Prednisolone / Q000378:metabolism*; D013237:Stereoisomerism
chemical_list: D009243:NAD; D011239:Prednisolone; D003903:Deuterium; D006913:Hydroxysteroid Dehydrogenases