Regulation of hydroxylations in biosynthesis of bile acids. Isolation of a protein from rat liver cytosol stimulating reconstituted cholesterol 7 alpha-hydroxylase activity.
Modulation of cholesterol 7 alpha-hydroxylase activity was studied in a purified, reconstituted system from rat liver microsomes. Cysteine, dithiothreitol, reduced glutathione, and thioredoxin activated the system whereas glutathione disulfide inactivated it. A protein, which stimulated cholesterol 7 alpha-hydroxylase activity in the presence of glutathione or thioredoxin, was purified to apparent homogeneity from rat liver cytosol. It has a minimum Mr of 25,000. The protein had no effect on 12 alpha-hydroxylation of 7 alpha-hydroxy-4-cholesten-3-one or 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. The cholesterol 7 alpha-hydroxylase stimulatory protein could not be replaced by the thioltransferase-dependent disulfide-reducing system nor by glutathione S-transferase A, B, or C. Neither ATP and MgCl2 nor sodium fluoride had any effect on the activity of the cholesterol 7 alpha-hydroxylase stimulatory protein. The results show that purified cholesterol 7 alpha-hydroxylase can be regulated by a mechanism involving disulfide bonds in the cytochrome P-450 molecule.
D000818:Animals; D001647:Bile Acids and Salts / Q000096:biosynthesis*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005978:Glutathione / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism; D006900:Hydroxylation; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013466:Sulfurtransferases / Q000378:metabolism
D001647:Bile Acids and Salts; D011506:Proteins; D013250:Steroid Hydroxylases; D002790:Cholesterol 7-alpha-Hydroxylase; D005982:Glutathione Transferase; D013466:Sulfurtransferases; D005978:Glutathione