Evolution of Purine-Degrading Enzymes in Animal Peroxisomes

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  • 動物ペルオキシソームにおけるプリン分解酵素群の進化

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Abstract

The end product of purine metabolism varies from species to species. The degradation of purines to urate is common to all animal species, while the degradation of urate is much less complete in higher animals. The comparison of subcellular distribution, intraperoxisomal localization forms, molecular structures and some other properties of urate-degrading enzymes (uricase, allantoinase and allantoicase) among animals is described. Liver uricase is located in the peroxisomes in all animals with uricase. On the basis of the comparison of intraperoxisomal localization forms, molecular weights, and solubility of liver uricase among animals, it is suggested that amphibian uricase is a transition form in the evolution of aquatic animals to land animals. Allantoinase and allantoicase are different proteins in fish liver, whereas the two enzymes form a complex in amphibian liver. The subcellular localization of allantoinase and allantoicase varies among fishes. Hepatic allantoinase is located both in the peroxisomes and in the cytosol in marine fishes, and only in the cytosol in fresh water fishes. Hepatic allantoicase is located on the outer surface of the peroxisomal membrane in the mackerel group and in the peroxisomal soluble matrix in the sardine group. Amphibian hepatic allantoinase-allantoicase complex is probably located in the mitochondria. On the basis of the previous data, changes of allantoinase and allantoicase in the molecular structure and intracellular localization during animal evolution may be as follows: fish liver allantoinase is a single peptide with a molecular weight of 54,000 and is located both in the peroxisomes and in the cytosol, or only in the cytosol. Fish liver allantoicase consists of two identical subunits with a molecular weight of 48,000 and is located in the peroxisomal soluble matrix or on the outer surface of the peroxisomal membrane. The evolution of fishes to amphibia resulted in the dissociation of allantoicase into subunits and in the association of allantoinase with the subunit of allantoicase. This amphibian enzyme was lost by further evolution.

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