Urea cycle enzymes and glutamate dehydrogenase inXenopus laevis andBufo viridis adapted to high salinity

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Abstract
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.