Urea synthesis in the lungfish: relative importance of purine and ornithine cycle pathways

The relative importance of the purine pathway (uricolysis) and the ornithine cycle as routes for urea synthesis was assessed in isolated liver preparations from the African lungfish Protopterus dolloi. Incorporation of C(14)-labeled precursors into urea was used for comparison. Both pathways are present in the lungfish, but the ornithine cycle is quantitatively more important.