title: Partial characterization of placental 3 beta-hydroxysteroid dehydrogenase (EC 1.1.1.145), delta 4-5isomerase (EC 5.3.3.1) in human term placental mitochondria.
abstract: A partial characterization of human term placental 3 beta-HSDH in mitochondria is reported. Apparent KM of pregnenolone: 70 nM. A dose-dependent stimulation of 3 beta-HSDH by NAD+ or NADP+ was observed in the range from 10(-6) to 10(-3) M (KM value of NAD+: 20 microM). At equimolar concentrations NAD+ is more than 10-fold as effective a cofactor of the 3 beta-HSDH than NADP+. pH optimum: 9.5 (glycine-NaOH buffer). Temperature optimum 40-45 degrees C. A rapid loss of 3 beta-HSDH activity was found after preincubation of the enzyme at 37 degrees C after 30 min; less than 50% of initial enzyme activity is present. No inhibition was obtained by Mg2+, Ca2+ Sr2+ and Ba2+ (1-100 mM). A strong inhibition was achieved with 1 mM Zn2+, Cd2+, Cu2+ and 10 mM and 100 mM Fe2+, Mn2+, Co2+ and Ni2+.
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007535:Isomerases / Q000378:metabolism*; D007700:Kinetics; D008670:Metals / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011284:Pregnenolone / Q000378:metabolism; D013251:Steroid Isomerases / Q000378:metabolism*; D013696:Temperature
chemical_list: D008670:Metals; D009243:NAD; D009249:NADP; D011284:Pregnenolone; D015096:3-Hydroxysteroid Dehydrogenases; D007535:Isomerases; D013251:Steroid Isomerases