動物の尿酸分解酵素群に関する研究 : Ureidoglycollate lyase の進化

Abstract

In lower animals such as marine invertebrates and crustaceans, urate is degraded to NH_3 and CO_2 as follows. Urate is degraded to allantoin by uricase (EC1.7.3.3); allantoin is then degraded by allantoinase (EC3.5.2.5) to allantoate, which is degraded to ureidoglycollate and urea by allantoicase (EC3.5.3.4). Ureidoglycollate is further degraded to glyoxylate and another molecule of urea by ureidoglycollate lyase (EC4.3.2.3). Urea formed is degraded to NH_3 and CO_2 by urease (EC3.5.1.5). However, the degradation of urate is much less complete in higher animals. It is generally accepted that during animal evolution, all of the urate degrading enzymes (uricase, allantoinase, allantoicase, ureidoglycollate lyase and urease) were lost in humans, anthropoid apes and New World monkeys, and all of the allantoin-degrading enzymes (allantoinase, allantoicase, ureidoglycollate lyase and urease) were lost in other mammals. However, surprisingly, ureidoglycollate lyase has been found in livers of rat, bovine and monkey, and in various tissues of rat. Ureidoglycollate lyase was highly purified and characterized from the heavy mitochondrial fraction of rat, bovine and monkey liver. The apparent Km values of the mammalian enzymes for ureidoglycollate were much higher than that of fish liver ureidoglycollate lyase. The mammalian enzymes differed from the fish liver enzyme in enzymic, physical and immunological properties.