Constitutive testosterone 6 beta-hydroxylase in rat liver.
The cytochrome P-450 that was purified from hepatic microsomes of male rats treated with phenobarbital and designated P450 PB-1 (Funae and Imaoka (1985) Biochim. Biophys. Acta 842, 119-132) had high testosterone 6 beta-hydroxylation activity (turnover rate, 13.5 nmol of product/min/nmol of P-450) in a reconstituted system consisting of cytochrome P-450, NADPH-cytochrome P-450 reductase, cytochrome b5, and a 1:1 mixture of lecithin and phosphatidylserine in the presence of sodium cholate. In ordinary conditions in the reconstituted system with cytochrome P-450, reductase, and dilauroylphosphatidylcholine, P450 PB-1 had little 6 beta-hydroxylase activity. The catalytic activities toward testosterone of two major constitutive forms, P450 UT-2 and P450 UT-5, were not affected by cytochrome b5, phospholipid, or sodium cholate. P450 PB-1 in rat liver microsomes was assayed by immunoblotting with specific antibody to P450 PB-1. P450 PB-1 accounted for 24.4 +/- 5.6% (mean +/- SD) of the total spectrally-measured cytochrome P-450 in hepatic microsomes of untreated adult male rats, and was not found in untreated adult female rats. P450 PB-1 was induced twofold with phenobarbital in male rats. P450 PB-1 was purified from untreated male rats and identified as P450 PB-1 from phenobarbital-treated rats by its NH2-terminal sequence, peptide mapping, and immunochemistry. These results showed that P450 PB-1 is a constitutive male-specific form in rat liver. There was a good correlation (r = 0.925) between the P450 PB-1 level and testosterone 6 beta-hydroxylase activity in rat liver microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)
Imaoka
S
S
Laboratory of Chemistry, Osaka City University Medical School.
Terano
Y
Y
Funae
Y
Y
D000818:Animals; D019826:Cholic Acid; D002793:Cholic Acids / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis* / Q000302:isolation & purification / Q000502:physiology; D003573:Cytochrome b Group / Q000494:pharmacology; D015786:Cytochromes b5; D005260:Female; D006801:Humans; D007120:Immunochemistry; D007527:Isoenzymes / Q000302:isolation & purification / Q000502:physiology; D008862:Microsomes, Liver / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology; D010743:Phospholipids / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000032:analysis*
D002793:Cholic Acids; D003573:Cytochrome b Group; D007527:Isoenzymes; D010743:Phospholipids; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C022657:steroid hormone 6-beta-hydroxylase; D019826:Cholic Acid; D010634:Phenobarbital