Origin and Possible Significance of Alanine Production by Skeletal Muscle.

摘要

These experiments were undertaken to determine the source of alanine released by skeletal muscle and to clarify the possible relationships between this process and the degradation of branched chain amino acids, the release of glutamine, and protein turnover in this tissue. During incubation in vitro, the rat diaphragm underwent net protein breakdown and released amino acids into the medium at a linear rate. The diaphragm released larger amounts of alanine and glutamine and lower amounts of leucine, isoleucine, and valine than would be expected from the average composition of muscle protein. Addition of the branched chain amino acids increased the production of alanine, glutamate, lysine, but not glutamine by the diaphragm in a concentration-dependent manner. At the same time, the branched chain amino acids inhibited net protein breakdown; therefore the increased amounts of alanine, glutamate, and lysine must have resulted from denovo synthesis or reduced catabolism of these amino acids. All the other amino acids together failed to increase the production of alanine or glutamate. Alanine production in muscle appears related to the rapid oxidation of the branched chain amino acids.