A novel NADP(+)-dependent dehydrogenase activity for 7alpha/beta- and 11beta-hydroxysteroids in human liver nuclei: A third 11beta-hydroxysteroid dehydrogenase.
Human tissue from uninvolved liver of cancer patients was fractionated using differential centrifugation and characterized for 11betaHSD enzyme activity against corticosterone, dehydrocorticosterone, 7alpha- and 7beta-hydroxy-dehydroepiandrosterone, and 7-oxo-dehydroepiandrosterone. An enzyme activity was observed in nuclear protein fractions that utilized either NADP(+) or NAD(+), but not NADPH and NADH, as pyridine nucleotide cofactor with K(m) values of 12+/-2 and 390+/-2microM, compared to the K(m) for microsomal 11betaHSD1 of 43+/-8 and 264+/-24microM, respectively. The K(m) for corticosterone in the NADP(+)-dependent nuclear oxidation reaction was 102+/-16nM, compared to 4.3+/-0.8microM for 11betaHSD1. The K(cat) values for nuclear activity with NADP(+) was 1687nmol/min/mg/micromol, compared to 755nmol/min/mg/micromol for microsomal 11betaHSD1 activity. Inhibitors of 11betaHSD1 decreased both nuclear and microsomal enzyme activities, suggesting that the nuclear activity may be due to an enzyme similar to 11betaHSD Type 1 and 2.
Department of Animal Science, The Hebrew University of Jerusalem, Rehovot, Israel. robinzon@agri.huji.ac.il
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Robinzon
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D042842:11-beta-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
D007527:Isoenzymes; D009243:NAD; D009249:NADP; D042842:11-beta-Hydroxysteroid Dehydrogenases