Lipid-Protein Interactions in the Reconstitution of the Microsomal Reduced Nicotinamide Adenine Dinucleotide-Cytochrome b5 Reductase System

Abstract

Abstract Interactions between the lipid bilayer and the hydrophobic portions of cytochrome b5 and NADH-cytochrome b5 reductase have been found to be essential for, and, in fact, to control the over-all rate of reduction of cytochrome b5 by NADH in hepatic microsomes. The present data and earlier work from this laboratory show that the reoxidation of reduced cytochrome b5 reductase by cytochrome b5 is the rate-limiting step in the reduction of microsomal cytochrome b5. Removal of phospholipid markedly decreases the rate of cytochrome b5 reduction and reconstitution with liposomes completely restores the structural and functional characteristics of the NADH-cytochrome b5 reductase electron transport pathway. These findings, along with the observation of a similar effect of liposomes on the NADH-dependent reduction of purified cytochrome b5 by the purified reductase, indicate that the amphipathic nature of these proteins is responsible for the lipid dependence of this reaction.