Random distribution of NADPH-specific flavoprotein and cytochrome P-450 in liver microsomes

Abstract

The dilution of rabbit liver microsomes by soy-bean phospholipids was used as methodical approach to investigate the molecular organization of NADPH-dependent microsomal redox chain. The ultrastructural analysis of control and phospholipid diluted microsomes revealed that the incorporation of exogenous phospholipids into microsome membranes increased their surface area, as well as decreased the lateral density distribution and size of intramembrane particles. The dilution of microsome membranes by phospholipids slowed down the initial rate of cytochrome P-450 reduction by NADPH. The apparent second order rate constant of cytochrome P-450 reduction by NADPH: cytochrome P-450-reductase did not change in phospholipid-enriched microsomes. The results obtained provide strong evidence for the random distribution of NADPH-specific flavoprotein and cytochrome P-450 in liver microsome membranes.