Abstract
Publisher Summary This chapter examines binding of cholesterol and adrenodoxin to phospholipid vesicle-reconstituted P-450 SCC. The side-chain cleavage of cholesterol requires 3 protein components: (1) cytochrome P-450 SCC , (2) adrenodoxin reductase (AR), and (3) adrenodoxin (ADX). The cytochrome catalyses a triple hydroxylation of cholesterol causing the scission of the 20–22 bond; the FAD-protein (AR) and the iron sulfur protein (ADX) serve as an electron transport chain to P-450. The chapter discusses the mechanism by which these proteins transfer electrons is investigated: AR forms a complex with ADX; the AR receives an electron pair from NADPH and transfers one electron to ADX. Reduction of ADX induces dissociation of the complex and allows interaction of the ADX with cytochrome—simultaneous interaction of ADX with AR and cytochrome does not occur. Binding of cholesterol to cytochrome induces a 20-fold increase in the binding of ADX and vice versa. These studies proposed that mutually facilitated binding of components prevents cytochrome P-450 from functioning as a futile NADPH or adrenodoxin oxidase.
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