PROTEIN-PROTEIN AND LIPID-PROTEIN INTERACTIONS IN A RECONSTITUTED LIVER MICROSOMAL MONOOXYGENASE SYSTEM

Abstract

This chapter analyzes protein–protein and lipid–protein interactions in a reconstituted liver microsomal monooxygenase system. As the hepatic microsomal monooxygenase system was resolved into two protein components, namely, cytochrome P-450 (cyt. P-450) and NADPH-cytochrome P-450 reductase (reductase), and phospholipid, these two protein components have recent been purified to homogeneous states. Successful reconstitution of monooxygenase systems on artificial phospholipid membranes has been reported. In this study, reductase and cyt P-450 purified from liver microsomes of phenobarbital-pretreated rabbits were incorporated into synthetic dimyristoyl phosphatidylcholine vesicles. The influence of gel to liquid-crystalline phase transition of this phospholipid on various activities catalyzed by these reconstituted systems was studied. When this reconstituted system was examined by negative-staining electron microscopy, the formation of single-walled vesicles, the diameters of which were about 500, was verified. The results obtained support the conclusion that the reduction of cyt P-450 by reductase is a diffusion-limited process and, in addition, suggest that the phospholipid environment can affect the conformation of cyt P-450.