Lipid composition of heart muscle homogenate.

Using cytochrome oxidase and esterase assays as a guide, mitochondria and microsomes were prepared from ox heart homogenate with about 25% cross-contamination of phospholipid. By the same criteria, the lipid complement of well washed myofibrils was essentially microsomal in origin. Approximately 60% of the phospholipid of the whole homogenate was found to be associated with microsomes, about half of this being firmly bound to myofibrils. Mitochondrial lipids were characterized by a higher degree of unsaturation of the free fatty acids and higher contents of cardiolipin, cholesterol, and coenzyme Q than in microsomes, where choline-containing phospholipid, especially sphingomyelin, formed a greater proportion of the total phospholipid than in mitochondria. The outstanding difference was the virtual localization of ethanolamine plasmalogen in microsomes, in contrast to the equal distribution of choline plasmalogen between mitochondria and microsomes. Myofibril lipids resembled more closely microsomal than mitochondrial lipids, but contained in addition phosphatidyl serine and phosphoinositide, which were not detected in mitochondria and microsomes.