Phospholipid and enzyme arrangements of rat liver rough microsomal subfractions from control and...

Rough microsomes from rat liver of both control and methylcholanthrene-treated animals were subfractionated on a discontinuous sucrose gradient into three fractions according the their sedimentation velocity. The slowly sedimenting vesicles were enriched in electron transport enzymes, while those in the pellet showed higher phosphatase and ATPase activities. Methylcholanthrene treatment introduced typical changes in enzyme composition, mainly an increase of the cytochrome P-448. The individual phospholipids exhibited an identical distribution pattern in the three subfractions and no change occurred after induction with methylcholanthrene treatment. Nearest neighbour analysis of phosphatidylethanolamine with dinitrodifluorobenzene revealed a similar pattern in the enzymatically different subfraction, that is, no cross-linking with phosphatidylserine occurred. One-third of the phosphatidylethanolamine was in monomer and dimer form and about two-thirds was protein linked. When membrane and enzyme synthesis was induced, cross-linking to proteins were substantially decreased. The experiments indicate that the phospholipids are distributed in a homogenous fashion in the lateral plane of the rough microsomal membrane and do not support the possibility that phosphatidylethanolamine is specifically associated with cytochrome P-450.