Urea cycle enzymes and glutamate dehydrogenase in Xenopus laevis and Bufo viridis adapted to high salinity.

Xenopus laevis was adapted stepwise to 600 m osmolar sodium chloride. After adaptation, the level of argininosuccinate lyase was raised 9-fold, carbamoylphosphate synthetase 6-fold, and ornithine carbamoyltransferase and arginase 3-fold. Liver glutamate dehydrogenase was also raised 5-fold; kidney glutamate dehydrogenase was unchanged. In Bufo viridis similarly adapted, there was a 5-fold increase in argininosuccinate lyase. When Xenopus laevis was adapted to 600 m osmolar sucrose, there was only an increase in argininosuccinate lyase, and that was only 2.4-fold. This indicates that the increases in urea cycle enzymes are at least in part responses to sodium chloride rather than just to osmotic stress.