THE REGULATION OF UREA-BIOSYNTHESIS ENZYMES IN VERTEBRATES
- 1 July 1965
- journal article
- research article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 96 (1), 28-35
- https://doi.org/10.1042/bj0960028
Abstract
Carbamoyl phosphate synthetase, orni-thine transcarbamoylase, the arginine-synthetase system and arginase were measured in the livers of ammoniotelic, ureotelic and uricotelic animals. The chelonian reptiles, whose nitrogen excretory patterns vary according to the habitat, and the Mexican axolotl, a neotenic species, were also studied. The levels of the activities of the first 3 enzymes mentioned correlate with the amount of N excreted as urea. The terrestrial turtle, which excretes mainly uric acid, maintains a high arginase activity but has very low levels of the activities of the other 3 enzymes. The first 3 enzymes of the urea cycle vary in the phylogenic scale in a co-ordinated manner, which suggests that they are under the same regulatory mechanism. Urea formation from endogenous arginine in vitro has a low efficiency in the Mexican axolotl. The induction of metamorphosis in the Mexican axolotl by the administration of L-triiodothyronine, which causes a shift from ammonio-ureotelism to complete ureotelism, is accompanied by an increase mainly in carbamoyl phosphate synthetase and also by an improvement in the efficiency of hydrolysis of endogenous arginine in vitro to give urea. The results obtained by differential centrifuga-tion of the urea-cycle enzymes in rat and Mexican-axolotl livers are presented. The location requirements for the integration of a metabolic cycle are discussed.Keywords
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