Abstract
AbstractActivities of arginase, xanthine dehydrogenase, and uricase were measured in liver and kidney of adult Phyllomedusa sauvagei and P. hypochondrialis to examine the enzymatic basis of their unusual ability to excrete uric acid. Comparable values were obtained for two species of ureotelic anurans and a uricotelic lizard. Both Phyllomedusa species exhibited high hepatic and renal levels of xanthine dehydrogenase, whereas this enzyme was not detected in the livers of the ureotelic frogs or the lizard. Hepatic xanthine dehydrogenase was significantly higher in P. sauvagei, which excretes urate predominantly, than in P. hypochondrialis, which excretes 20% of its nitrogen as urate. Hepatic arginase was much lower in both Phyllomedusa species than in the ureotelic frogs, but higher than in the lizard. Reduced levels of uricase were also associated with uricotelism in this genus.Xanthine dehydrogenase was present in livers of larval P. sauvagei well in advance of the onset of uric acid excretion late in metamorphosis. Premetamorphic larvae excreted over 50% of their nitrogen waste as urea and the balance as ammonia.
Published Version
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