FORMATION OF THE PEPTIDE CHAIN OF HEMOGLOBIN

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Abstract
Ribosomes labeled with C14-valine (the N-terminal amino acid of hemoglobin) were isolated from intact cells, incubated with C12-amino acids in the cell free system, and the labeled hemoglobin then isolated. In other experiments, unlabeled ribosomes were incubated with C14-valine and the labeled hemoglobin isolated. Comparisons were made of the radioactivity in N-terminal valine versus that in valine in the rest of the hemoglobin chain. The results indicate that hemoglobin is synthesized segmentally beginning at the N-terminal end of the chain and that incomplete sequences are present in the ribosome. It may be that the N-terminal amino acid is held to the ribosome through its amino group, the carbonyl group attached to transfer - RNA then joins with the amino group of the next amino acid eliminating the valine-bond transfer - RNA; the growing peptide chain terminating at all stages in amino acyl - RNA.