Urea formation in mammalian liver

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Abstract
Leuthardt''s observation that liver of starved guinea-pigs forms urea more rapidly from glutamine than from NH4Cl is confirmed, but the rate of urea formation from ammonium glutamate is of the same order as that from glutamine. The facts are in accordance with the view that ammonium glutamate is an intermediate in the urea formation from glutamine. It is therefore unnecessary to assume a more or less direct conversion of the amide N of glutamine into urea, as postulated by Leuthardt. The ability of kidney cortex to synthesize arginine from citrulline and glutamate, discovered by Borsook and Dub-noff, is confirmed. The synthesis does not occur in the liver and therefore cannot be responsible for the accelerating effect of glutamate on the urea synthesis in this tissue. Bach''s statement that a-ketoglutarate and pyruvate increase the rate of urea formation from citrulline and from ornithine is not confirmed. The discrepancy is assumed to be due to exptl. errors in Bach''s procedure. The results of Trowell, who claimed to have found that under certain conditions arginine and citrulline do not behave in the manner postulated by the ornithine cycle theory, are discussed, and reasons are given which show that Trowell''s findings are not contradictory to the theory.

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