INSULIN AND INCORPORATION OF AMINO ACIDS INTO PROTEIN OF MUSCLE. 2. ACCUMULATION AND INCORPORATION STUDIES WITH THE PERFUSED RAT HEART

Abstract

The accumulation and incorporation into protein of C14-labelled amino acids by the perfused rat heart and the effect of insulin thereon has been studied. The entry of label into intracellular water was usually observed within a few minutes, and might continue to rise for as long as 80 min. or reach a constant concentration in as short a period as 10 min. Accumulation was decreased in various degrees by cyanide, azide and anoxia. The accumulation of glycine, proline and [alpha]-aminoisobutyric acid was stimulated by insulin; that of alanine, valine, lysine, glutamic acid, phenylalanine and tyrosine was not. Insulin stimulated the incorporation into protein of each of 4 amino acids studied (glycine, proline, lysine and glutamic acid). The rate of incorporation of amino acids into protein was fairly constant through- out the perfusion, despite a continual rise in the amount of radio-activity accumulated. With diaphragm some evidence of a lag in the onset of incorporation during the initial accumulation of glycine and proline was observed. The results do not support the concept that insulin stimulates the incorporation of amino acids into protein of muscle solely through an enhancement of their accumulation, nor are they entirely consistent with the view that the amino acids entering are derived from a pool functionally distinct from the total free amino acids of the tissue.