Studies on myocardial metabolism of protein and amino acids by the use of C14-labelled substrates.

(1) In order to study the relationship between the energy metabolism via TCA cycle and amino acid metabolism as well as protein synthesis, C14-labelled substrates were used for tracer experiment . (2) Considerable C14O2 formation was noted from carbohydrates such as acetate-1-C14, pyruvate-1-C14, and pyruvate-3-C14, while a smaller amount of C14O2 was produced from amino acids such as glycine1-C14, alanine-1-C14, and glutamic acid-1-C14. Since glutamine-C14(U) was a universal type, a direct comparison with other labelled substrates was not possible, but a considerable amount of C14O2 production was noted. (3) The transfer from acetate-1-C14 to glutamic acid, from pyruvate3-C14 to alanine and glutamic acid suggests the presence of the process of formation of glutamic acid from TCA cycle in the myocardium. (4) Comparison between pyruvate-1-C14 and pyruvate-3-C14 revealed more transference of -3-C14 to amino acid. (5) The carbon chains of glycine, alanine, and glutamic acid were transferred into other amino acids in the myocardium. Glutamine was also changed into many amino acids, and the transfer to glutamic acid was especially pronounced. (6) The increase in C14O2 production from carbohydrate and glutamine through digitalis administration might suggest the facilitation of the utilization of these substrates by digitalis. (7) Administration of ammonia inhibited oxidation of pyruvate3-C 14.