Cholesterol and phospholipid composition of mitochondria and microsomes isolated from morris hepatoma 51 23 and rat liver

Abstract

The major component of membranous lipids is represented by phospholipids [l] . It is well known that this class of lipids plays an important role in regulating the biochemical properties of subcellular particles [2] . Moreover, there exists a cholesterol:phospholipid ratio peculiar for several kinds of membranes [3]. Cholesterol is important in stabilizing arrays of phospholipids in cellular and cytoplasmic membranes [4,5] , and in regulating the permeability to small molecules of artificial [6,7] and natural [8] membranes. Lipid-lipid interactions play an important role in the interaction between lipid and protein [3] ; the protein conformation is greatly influenced by their association with the lipid environment [9]. Alterations in the protein components of mitochondrial membranes have been observed in hepatoma mitochondria [ 10,l l] . They could be, at least in part, explained by changes in the lipid composition of membranes. In hepatoma mitochondria, we have also found functional changes, which could be related to high fragility and to an increased resistance to deformation and stretching [ 12,131 . Similar alterations have been observed also in cholesterol-enriched mitochondria [5] . The knowledge of lipid composition of membranes isolated from tumors is lacking and, sometimes, contrasting [ 14,151 . As a first approach to this problem we have studied the phospholipid and cholesterol content of mitochondria and microsomes isolated from rat liver and Morris hepatoma 5 123. 2. Methods