Urea Cycle and Pyrimidine Synthesis in Elasmobranchs

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Elasmobranchs (sharks, skates, and rays) are a group of primitive fishes which synthesize and retain in their tissues high levels of urea for the purpose of counteracting the high salt concentration of seawater. Our studies have shown that the pathway for urea synthesis in sharks is uniquely different from the urea cycle in mammalian species, which excrete nitrogen waste products as urea. Other significant differences in related metabolic pathways have also been discovered. The purpose of this study is to 1) characterize these unique properties and relate the results to the adaptive metabolic strategies of elasmobranchs and osmoregulation and 2) relate these unique metabolic properties of the sharks. The results will contribute to understanding of metabolic adaptation and evolution, and of the significance of the different pathway for urea synthesis relative to regulation of osmolarity in a seawater environment.