Utilization of serum-protein-bound glycine in the formation of globin and haem

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Abstract
Rats were injected intravenously with rat serum globulin or serum albumin obtained from donor animals injected with [2-14C]glycine and the incorporation of serum-protein-bound glycine into haem and globin was followed for 15 days. Serum-protein-bound glycine was utilized efficiently both as a source of glycine by the protein globin and as a precursor in the formation of haem. The specific activities of haem and globin glycine indicated that the injected protein was broken down to free amino acids prior to the incorporation of the glycine into the globin. On breakdown of serumprotein, the extent of utilization of serum-protein-bound glycine in the formation of globin and haem was less than or equal to that of injected free glycine, a finding in contrast with those previously reported for other systems in which free amino acids may not be the intermediates. About 1.4% of serum-protein-bound glycine was utilized as a source of globin glycine. This represents about 1% of the total glycine required in globin synthesis. Since serum proteins constitute only 2% of the rat''s total proteins, this contribution of serum-protein-bound glycine to globin biosynthesis appears to be significant.