Kinetic evidence for the involvement of a common enzyme in the microsomal reduction of retinal and androstenedione in rat liver.
Androst-4-ene-3,17-dione (androstenedione) was found to be a potent competitive inhibitor of the NADH-supported reduction of retinal in rat hepatic microsomes (Ki 42 microM, Km/Ki ratio 1.1). Similarly, the NADH-mediated reduction of androstenedione was inhibited in mixed fashion by retinal (Ki 12 microM, Km/Ki ratio 0.34). In subsequent experiments the cofactor NADH exhibited an identical Km (8 microM) in the microsomal reductions of both substrates. Acidic pH markedly stimulated the microsomal reduction of androstenedione to testosterone and was also found to enhance retinal reduction to retinol, although the latter reaction exhibited a distinct pH optimum between 6.0 and 6.5. These results suggest that a common enzyme may participate in the reduction of both substrates but at least one other enzyme probably participates in hepatic microsomal testosterone production.
Department of Medicine, University of Sydney, Westmead Hospital, NSW, Australia.
R
R
Martini
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M
Murray
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000037:antagonists & inhibitors; D000735:Androstenedione / Q000378:metabolism*; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D050697:Retinal Dehydrogenase; D012172:Retinaldehyde / Q000378:metabolism*
D009243:NAD; D000735:Androstenedione; D015067:17-Hydroxysteroid Dehydrogenases; D000445:Aldehyde Oxidoreductases; D050697:Retinal Dehydrogenase; D012172:Retinaldehyde