Experimental injury and sulfur amino acid metabolism.

It has been reported that methionine and cystine are capable of accelerating the healing rate of wounds in injured rats to the same extent when present in the diet in equivalent amounts (1). This response was elicited in both the presence and the absence of dietary protein (2). Lysine, tryptophan, and valine do not appear to alter the healing process to a significant degree (3). Because methionine is converted to cystine, although the reverse reaction does not occur to an appreciable extent in viva (4, 5), it was suggested that cystine might be the more limiting amino acid for the healing of experimental wounds (1). This supposition appears to have been substantiated from analyses of wounded and corresponding unwounded skin tissue. When healing is thought to be essentially complete, i.e. when the nitrogen content of wounded and corresponding normal tissue is similar (6), the cystine level in the former is 2.5 times that of the normal tissue, and the methionine content has also increased, but to a lesser degree (2). The excessive demand for the sulfur-containing amino acids by regenerating wound tissue, along with the negative nitrogen balance characteristic of injury, suggests rather strongly that the phenomena of wounding and regeneration markedly influence protein metabolism. A previous report dealt with the incorporation of V6-labeled methionine and cystine into various tissues after experimental injury (2). The effect of injury on sulfur amino acid metabolism will be considered in the present paper.