Lipid-protein interactions in mitochondria: III. Solvent extraction of phospholipids from mitochondrial preparations

Abstract

Monohydric alcohols extract phospholipids from beef heart mitochondria and submitochondrial particles with an efficacy which depends on the chain length of the alcohol. MgCl 2 and CaCl 2 prevent alcohol extraction of part of the phospholipids. All particles used are affected by alcohols to similar extents. Diethyl ether extracts phospholipids from sonicated phospholipid vesicles in presence of NaCl or at acid pH even when the vesicles were bound to lipid-depleted mitochondria; ether extracts little phospholipid from beef heart mitochondria or submitochondrial particles under similar conditions; NaSCN is however much more effective than NaCl in increasing the extractability of phospholipids by ether. Mitochondrial membranes treated with 10 m m HCl are freed of the soluble proteins and of the proteins of the ATPase complex; phospholipids can be extracted in large amounts from such membranes by ether in presence of salt. Detachment of the ATPase complex from mitochondria by other means also results in higher phospholipid extractability by ether. Lyophilized mitochondria or submitochondrial particles can be extracted of phospholipids by means of ether or pentane only after HCl treatment. Chloroform-methanol 2:1 extracts phospholipids and a small but significant portion of the protein from mitochondria and various mitochondrial preparations. The possible presence of proteolipids is discussed. The results of this investigation are discussed in relation to the importance of hydrophobic interactions between phospholipids and proteins in mitochondria; hydrophobic bonds however are not unique and the hypothesis is advanced that superficial proteins are linked to the mitochondrial membrane by other types of bonds.