Incorporation of arginine by a soluble system from sheep thyroid

During an investigation of protein synthesis by cell-free extracts from thyroid, it became evident that incorporation of arginine differed from that of other amino acids and could proceed by two separate mechanisms. One depended on the presence of both ribosomes and a supernatant fraction, whereas the other required only the supernatant fraction. This report describes the properties of the soluble system for incorporation of arginine. The reaction is dependent on an energy source and supplementary S-RNA. Arginyl S-RNA is an intermediate. The transfer of arginine from S-RNA into hot TCA-insoluble material does not require magnesium ions and is not inhibited by puromycin. The product of the reaction is made acid-soluble by trypsin but not by RNAase.