Investigations into the interrelationships between energy metabolism (oxidative phosphorylation), characteristics and specificity of biological membranes and intracellular metabolic regulation will be studied at several levels of tissue organization. Isolated perfused rat hind quarters and hearts will be employed further to evaluate both qualitative and quantitative aspects of anaplerotic reactions to the citric acid cycle in muscle. The effects of diet and physicological state on these pathways will be evaluated. The NAD-NADP-specific 'malic' enzymes which we have observed to be a heart mitochondria will be further characterized. The transfer of reducing power across the mitochondrial membrane is mediated by substrate shuttle systems which are regulated by exchange enzymes in the membrane and, in turn, by the 'energy-pressure' of the system. Cell-free in vitro systems containing liver mitochondria and cytoplasmic enzymes and a 'physiological' energy load and, later, isolated whole hepatocytes will be used to evaluate the coupling between energy metabolism, substrate anion transport, intracellular transfer of reducing power and the control of major pathways such as gluconeogenesis and lipogenesis. BIBLIOGRAPHIC REFERENCES: L. Lumeng, J. Bremer, and E. Jack Davis, "Suppression of the Mitochondrial Oxidation of (minus) Palmitylcarnitine by the Malate-Aspartate and alpha-Glycerolphosphate Shuttles. J. Biol. Chem., in press (Jan. 1976). J. Bremer and E. Jack Davis, "Studies on the Active Transfer of Reducing Equivalents into Mitochondria via the Malate-Aspartate Shuttle". Biochim. Biophys. Acta 376, 387-397 (1975).