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1. Mitochondria, inner and outer mitochondrial membranes and microsomes were isolated and purified from pig heart. Their lipid composition and protein components were studied. 2. The fatty acid distribution in the main phospholipids seemed specific rather of a given phospholipid and not of one type of membrane. 3. Inner mitochondrial membranes were characterized by a high content in cardiolipin and a very low level of triglycerides together with a high degree of unsaturation and C18 acids. Gel electrophoresis revealed 13 different polypeptide subunits of which 5 were major ranging in molecular weights from 10000 to 215000. 4. In outer mitochondrial membranes, total lipid, phosphatidylcholine, phosphatidylinositol, plasmologen and triglyceride contents were much higher than in inner membranes. Fatty acids of phospholipids were mostly saturated and the polypeptide pattern showed 12 components, of which 4 were major of mol. wt 75000, 60000, 20000 and below 10000. 5. Compared to outer membrane, microsomes exhibited a much higher cholesterol content and markedly different protein profiles. They contained significant amounts of cardiolipin and phosphatidylserine, this latter phospholipid being exclusively located in microsomes. However odd similarities were observed in some lipid components of microsomes and inner mitochondrial membranes, but fatty acids were more saturated in microsomes and electrophoretic profiles of protein components appeared very different and revealed components of high mol. wt.

Abnormalities have been noticed in the phospholipid and cholesterol composition of the atrophied gastrocnemius muscle of frog denervated for 1 month. Cholesterol : phospholipid molar ratios in the muscle increased on denervation. Sphingomyelin and cardiolipin fractions increased in contrast to phosphatidyl choline, phosphatidyl serine and phosphatidyl ethanolamine in the sarcoplasmic reticulum (SR) of denervated muscle. Na-azide sensitive Ca2+ ATPase activity of the mitochondria did not alter whereas that of SR decreased on denervation. Phospholipase C digestion impaired the organelle Ca2+-ATPase activity. The above abnormalities in enzyme activities have been correlated to the changes in the lipid composition of the denervated muscle. On the basis of these changes it is discussed that the primary change in the muscle due to denervation is the change in the permeability of the membrane.