THE INCORPORATION OF RADIOACTIVE LYSINE OR TYROSINE INTO CARDIAC AND SKELETAL MYOFIBRILLAR AND NON - MYOFIBRILLAR CONTRACTILE PROTEINS

Abstract

The labeled amino acids incorporation into cardiac and skeletal contractile proteins was compared after a single injection of 3H-lysine, repeated injections of 3H-lysine during 1 or 6 h or after a continuous infusion of both 3H-lysine and 14C-tyrosine. The myofibrillar incorporation was higher in the heart than in the skeletal muscle. Myosin H chains and actin were prepared using gel filtration. The incorporation was again higher in the heart for these proteins but the labeling of actin in both the muscles rapidly reaches a plateau in contrast with myosin. These 2 proteins apparently possess a different precursor pool. Myosin H chains prepared from the supernatant obtained after a relaxing treatment were more labeled than those extracted from myofibrils. These H chains from the supernatant were presumably newly synthetized and not yet incorporated into myofibrils. They were more labeled in the heart than in the skeletal muscle. The myosin synthesis itself was different and not the process of assembly of the myofibrils.