This proposal outlines our experimental approach to three important regulatory problems involved in liver metabolism. The first of these problems concerns the characterization of a regulatory relationship between the ketogenic and gluconeogenic pathways mediated by the mitochondrial monocarboxylate translocator. We have proposed that the exchange of mitochondrial acetoacetate for cytosolic pyruvate via the monocarboxylate translocator is a primary regulator of the supply of precursors for the gluconeogenic pathway. Several experiments are proposed to test and to elaborate upon this hypothesis in various liver-derived metabolic systems. Considerable effort will be given to the development of specific inhibitors of the monocarboxylate translocator with an ultimate goal of isolating and characterizing the molecular properties of this important mitochondrial substrate transport system. Second, we have proposed studies to define certain aspects of the regulatory effects of Alpha-adrenergic agonists such as epinephrine in the liver. Experiments have been suggested a) to define the source of the calcium ions which are released into the liver cytosol upon Alpha-stimulation and b) to characterize the effects of Alpha-adrenergic stimulation on various mitochondrial processes. Finally, the regulatory properties of the hepatic glycine cleavage system will be investigated in perfused rat livers and in isolated liver mitochondria. The possible regulatory effects of various alternative substrates (e.g., fatty acids, amino acids and ketone bodies) and nucleotide species (e.g., adenine and pyridine nucleotides) will be assessed. Possible inhibitory effects of several compounds on mitochondrial glycine transport will be evaluated. Changes in the glycine cleavage system will be monitored in livers derived from animals in several nutritional/hormonal state (e.g., fed, fasted diabetic, etc.). Ultimately we would like to define the relationship between the activity of the glycine synthase multienzyme complex in the liver and various clinically defined hyperglycinemic states.
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