Metabolism of urea and glyoxylate, degradative products of purines in marine animals.
In marine fish and crustacean liver, degradative enzymes able to convert purines to urate have been shown to be located only in the cytosol, and degradative enzymes able to convert urate to urea and glyoxylate, only in the peroxisomes (Noguchi, T., Takada, Y., & Fujiwara, S. (1979) J. Biol. Chem. 254, 5272-5275). The subcellular distribution of these two enzymes involved in further metabolism of urea and glyoxylate in marine animal species was examined by centrifugation in a sucrose density gradient. Urease was located only in the cytosol of crustacean and mollusc liver; no activity was detected with fish liver. In fish, crustacean and mollusc liver, the conversion of glyoxylate to glycine may be mainly catalyzed by alanine : glyoxylate aminotransferase. Hepatic alanine: glyoxylate aminotransferase was located both in the mitochondrial matrix and in the cytosol in each species studied. These findings suggest that peroxisomal urea is transported to the cytosol then degraded to NH3 for the excretion of purine nitrogens, while peroxisomal glyoxylate is transported to the cytosol or mitochondria then converted to glycine for the reutilization of purine carbons.