Biochemical Studies on Amphibian Metamorphosis I. The effect of thyroxine on protein synthesis in the tadpole

Thyroxine has been shown to accelerate the synthesis of carbamyl phosphate synthetase in the liver of Rana catesbdana. Stimulation of carbamyl phosphate synthetase synthesis by thyroxine appears to be relatively specific because of the following observations: (I) succinoxidase activity decreased during the time that carbamyl phosphate synthetase increased; (2) liver catalase responded more slowly than carbamyl phosphate synthetase to thyroxine; (3) the ratio of biochemical changes/morphological changes was greatly altered during thyroxine-induced metamorphosis. The relationships between the concentration of thyroxine and (I) temperature; (2) duration of exposure of the tadpole to thyroxine; and (3) the activity of carbamyl phosphate synthetase during the induced synthesis of carbamyl phosphate synthetase by thyroxine are discussed. Chloramphenicol and thiouracil partly counteracted the effect of thyroxine on the synthesis of carbamyl phosphate synthetase. I N T R O D U C T I O N A characteristic of metamorphosis, in the animal kingdom in general, is that the polymorphic animal expresses itself in such a way that one form replaces another during the normal life of the individual. Amphibian metamorphosis, in particular, represents a preparation for the transition from an aquatic life during the larval stage to the terrestrial habitat in the adult. In preparation for this ecological transition, numerous anatomical and biochemical changes occur. The following biochemical changes have been studied in some detail: (a) transition of visual pigment from porphyropsin to rhodopsin (1); (b) character of hemoglobin (2); (c) plasma proteins (3); and (d) ammonotelism to ureotelism (4, 5). This study was supported in part by grants from the National Cancer Institute, National Institutes of Health, United States Public Health Service (No. C-3571); and the Wisconsin Alumni Research Foundation. Recdved for publication, June 5, 1959.