Incorporation in vivo of 15N-labeled glycine into liver fractions of newly hatched chicks

Abstract In the livers of newly hatched chicks, 15N from labeled glycine is incorporated in vivo into the microsome proteins earlier and at a more rapid rate than into the proteins of any other cell fraction isolated by differential centrifugation. The microsomes, moreover, probably contribute in a high degree to the surprisingly high isotope level of the considerable amounts of cell fluid proteins. Since the microsomes are especially rich in ribonucleic acid, and the production of phosphate-bound energy is centered in the mitochondria, the experiments indicate that the immediate availability of ribonucleic acid is more important for the formation of proteins than a close proximity to energy-producing enzyme systems.