title: Catalytic properties of cytochrome P-450scc from bovine and porcine adrenocortical mitochondria: effect of Tween20 concentration.
abstract: Cholesterol side-chain cleavage activities of cytochrome P-450ssc purified from bovine adrenocortical mitochondria were measured for various substrates, including cholesterol, 20[S]-hydroxycholesterol, 22[R]-hydroxycholesterol and 20[R], 22[R]-dihydroxycholesterol, in the reconstituted enzyme system at various Tween20 concentrations. The side-chain cleavage activity for cholesterol showed more than 10-fold enhancement upon addition of 0.1% Tween20, compared with that without the detergent. Addition of Tween20 did not cause any enhancement of the side-chain cleavage activities for 20[S]-hydroxycholesterol and 22[R]-hydroxycholesterol; rather, it resulted in an inhibition of the activities. The side-chain cleavage activity for 20[R],22[R]-dihydroxycholesterol showed a very high value even without the detergent. As the stimulatory effect of Tween20 was only specific for cholesterol, Tween20 seemed to enhance the rate of access of cholesterol to cytochrome P-450scc. These results are consistent with the suggestion that a transfer of substrate, cholesterol, in mitochondrial inner membrane, to the substrate-binding site of cytochrome P-450scc is the rate-limiting step in the cholesterol side-chain cleavage reaction.
authors.affiliation: Department of Biochemistry, Kagawa Medical School, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Iwahashi
authors.forename: M
authors.initials: M
authors.lastname: Tsubaki
authors.forename: A
authors.initials: A
authors.lastname: Miyatake
authors.forename: S
authors.initials: S
authors.lastname: Miura
authors.forename: K
authors.initials: K
authors.lastname: Hosokawa
authors.forename: Y
authors.initials: Y
authors.lastname: Ichikawa
mesh_terms: D000302:Adrenal Cortex / Q000648:ultrastructure*; D000818:Animals; D002384:Catalysis; D002417:Cattle; D002784:Cholesterol / Q000378:metabolism; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000378:metabolism*; D006888:Hydroxycholesterols / Q000378:metabolism; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D011136:Polysorbates / Q000008:administration & dosage / Q000494:pharmacology*; D013379:Substrate Specificity; D013552:Swine
chemical_list: D006888:Hydroxycholesterols; D011136:Polysorbates; C003563:20,22-dihydroxycholesterol; D002784:Cholesterol; D002786:Cholesterol Side-Chain Cleavage Enzyme