Deficiency of pyrroline-5-carboxylate synthase in the intestinal mucosa of the cat

Pyrroline-5-carboxylate synthase activity of the intestinal mucosa of cats was compared to that of rats and found to be only 18% as high per gram of mucosa and only 5% as high per kilogram body weight. This severe limitation in the first step in the de novo synthesis or ornithine may be the metabolic basis for the severe hyperammonemia found in cats fed an arginine-deficient diet. This lack of ornithine synthesis makes the cat completely dependent on dietary arginine for the ornithine required for the removal of ammonia via urea synthesis in the liver.