海棲動物種における Urease および Glyoxylate aminotransferase の細胞内分布

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The end product of purine metabolism varies from species to species. In human and other primates and birds, the end product is uric acid because they do not possess uricase (EC 1.7.3.3) activity. In mammals other than primates and some reptiles, the end product is allantoin ; uricase is responsible for the hydrolysis of uric acid to allantoin. In most fishes and amphibia, the allantoin formed is further degraded to urea and glyoxylate via allantoic acid by allantoinase (EC 3.5.2.5) and allantoicase (EC 3.5.3.4). In some marine invertebrates and crustaceans, the urea formed is hydrolyzed to NH_3 and CO_2 by urease (EC 3.5.1.5). In marine fish and crustaceous liver, degradative enzymes of purines to urate are located only in the cytosol and degradative enzymes of urate to urea and glyoxylate only in the peroxisomes (Noguchi, T., Takada, Y., and Fujiwara, S. (1979) J. Biol. Chem. 254, 5272-5275). Because the degradation of purines is much less complete in higher animals, it is apparent that certain peroxisomal enzymes have been lost during animal evolution, e.g. uricase, allantoinase and allantoicase. In the present study, the subcellular distribution of the two enzymes, involved in further metabolism of urea and glyoxylate, was examined by centrifugation in a sucrose density gradient with marine animal species. Urease was located only in the cytosol of crustaceous and mollusc liver ; the activity was not detected in fish liver. In fish, crustaceous and mollusc liver, the conversion of glyoxylate to glycine was suggested to be mainly catalysed by alanine : glyoxylate aminotransferase (EC 2.6.1.44). Hepatic alanine : glyoxylate aminotransferase was located both in the mitochondrial matrix and in the cytosol in each species. These findings suggest that peroxisomal urea is transported to the cytosol followed by its degradation to NH_3 for the excretion of purine nitrogens and peroxisomal glyoxylate to the cytosol or mitochondria followed by its conversion to glycine to bring a purine cycle to completion or for the reutilization of purine carbons.
九州歯科学会の論文
1982-06-25

海棲動物種における Urease および Glyoxylate aminotransferase の細胞内分布

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