The role of cytochrome b5 in adrenal microsomal steroidogenesis.
The role of cytochrome b5 in adrenal microsomal steroidogenesis was studied in guinea pig adrenal microsomes and also in the liposomal system containing purified cytochrome P-450s and NADPH-cytochrome P-450 reductase. Preincubation of the microsomes with anti-cytochrome b5 immunoglobulin decreased both 17 alpha- and 21-hydroxylase activity in the microsomes. In liposomes containing NADPH-cytochrome P-450 reductase and P-450C21 or P-450(17) alpha,lyase, addition of a small amount of cytochrome b5 stimulated the hydroxylase activity while a large amount of cytochrome b5 suppressed the hydroxylase activity. The effect of cytochrome b5 on the rates of the first electron transfer to P-450C21 in liposome membranes was determined from stopped flow measurements and that of the second electron transfer was estimated from the oxygenated difference spectra in the steady state. It was indicated that a small amount of cytochrome b5 activated the hydroxylase activity by supplying additional second electrons to oxygenated P-450C21 in the liposomes while a large amount of cytochrome b5 might suppress the activity through the interferences in the interaction between the reductase and P-450C21.
Kominami
S
S
Faculty of Integrated Arts and Sciences, Hiroshima University, Japan.
Ogawa
N
N
Morimune
R
R
De-Ying
H
H
Takemori
S
S
D000305:Adrenal Cortex Hormones / Q000096:biosynthesis*; D000311:Adrenal Glands / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D015786:Cytochromes b5 / Q000276:immunology / Q000494:pharmacology / Q000502:physiology*; D004579:Electron Transport / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006168:Guinea Pigs; D007074:Immunoglobulin G; D008081:Liposomes / Q000378:metabolism; D008297:Male; D008861:Microsomes / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism; D013255:Steroid 21-Hydroxylase / Q000378:metabolism
D000305:Adrenal Cortex Hormones; D007074:Immunoglobulin G; D008081:Liposomes; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D013255:Steroid 21-Hydroxylase; D013254:Steroid 17-alpha-Hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase