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Reutilization of Guanido-labeled Arginine in Rat Liver Proteins and the Influence of Diet¹

Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts 02115

The loss of L-[¹⁴C-guanido] arginine from liver proteins is thought to be a direct measure of liver protein catabolism since it is believed that the labeled arginine is only minimally reutilized to form liver protein. The retention of such labeled arginine is somewhat greater in the livers of rats fed a protein-free diet, suggestive of a reduced rate of protein catabolism. However, when 1.0 to 1.5% arginine was included in a protein-free diet the loss of activity was similar to that found in normally fed animals. It is concluded that the guanido-labeled arginine is reutilized to a considerable degree in energy- or protein-deficient animals and that this recycling can be minimized by feeding arginine. The inclusion of lysine in the restricted diet also had a significant effect upon the retention of labeled arginine.

KEY WORDS: • amino acid recycling • protein deficiency • liver protein metabolism

¹ Supported in part by Public Health Service Research Grants AM-09520 and K6-AM-18455 from the National Institutes of Health and the Fund for Research and Teaching, Department of Nutrition, Harvard School of Public Health.

Manuscript received 26 December 1973.