A study of ornithine, citrulline and arginine synthesis in growing chicks

Abstract

Citrulline-C 14, labeled in the ureido carbon, was fed to chicks maintained on a low arginine diet. About one-third of the isotope given was found in the amidine carbon of arginine isolated from tissue proteins. The results provide direct evidence that the chick does convert citrulline to arginine. Taken in conjunction with previous enzymatic findings, it becomes evident that the kidney and other extrahepatic tissues carry out the conversion and that the pathway followed is through argininosuccinate formation as with mammalian species. Further data indicate that the chick cannot convert ornithine to citrulline. This was shown by the absence of C 14 in tissue arginine after the administration of Na 2C 14O 3 together with unlabeled citrulline and a low arginine diet. Thus the indispensability of arginine in fowl nutrition and the absence of an ornithine cycle are both manifestations of the absence of the four enzymes of arginine synthesis from the liver. A new method for the isolation of ornithuric acid was applied to the investigation of ornithine synthesis. Evidence that the chick does not synthesize ornithine was shown by the absence of C 14 in the excreted ornithuric acid following the administration of sodium benzoate and glutamate-C 14 or Na 2C 14O 3 on a normal diet, or Na 2C 14O 3 on a low arginine diet.