Work

Amphibian allantoinase. Molecular cloning, tissue distribution, and functional expression.

Year: 1994

Type: article

Abstract: The chain of enzymes necessary to convert uric acid to its metabolic products urea and glyoxylic acid in vertebrates is truncated through the successive loss of allantoicase, allantoinase, and urate oxidase during phylogenetic evolution.Previous studies have assigned the localization of both urate oxidase and allantoinase to the peroxisome in the amphibian liver.This study reports the cloning of a cDNA encoding bullfrog (Rana catesbeiana) allantoinase, an enzyme that converts allantoin to allantoic acid.The cDNA is 2112 base pairs in length containing a 1449-base pair open reading frame which corresponds to a 483-residue protein (53,296 Da).Structural analysis of the deduced protein suggested two potential transmembrane segments and the presence of a putative mitochondrial localization sequence in the amino terminus.Immunocytochemical analysis revealed that allantoinase is localized to mitochondria and not to peroxisomes.On Northern blotting, a single mRNA species was detected in the liver and kidney of frog but not in other tissues; this distribution was confirmed by immunoblotting.The hepatic-and renal-specific expression of allantoinase coincides with the distribution of urate oxidase in these tissues in the frog.The allantoinase expressed in Saccharomyces cereuisiae and in Spodoptera frugiperda (Sf9) insect cells exhibits catalytic activity and is antigenically identical to the native frog enzyme.The degradation of purines to uric acid is common to all vertebrates; however, the catabolism of uric acid vanes from species to species (1).Urate oxidase (EC 1.7.3.31, a peroxisomal enzyme that catalyzes the oxidation of uric acid to allantoin, occupies a pivotal position in the chain of enzymes responsible for the metabolism of purines (1, 2).Hydrolysis of allantoin by allantoinase (EC 3.5.2.5) results in the formation of allantoic acid for further metabolism by allantoicase (EC 3.5.3.4) to yield urea and glyoxylic acid (1,3).The chain of these three enzymes responsible for the conversion of uric acid to urea, has become progressively truncated during evolution due to successive loss of allantoicase, allantoinase, and urate oxidase (1).Most mammals, with the exception of human and certain hominoid pri-R37 GM23750 and by the Joseph L. Mayberry Sr. Endowment Fund.

Source: Journal of Biological Chemistry

DOI: 10.1016/s0021-9258(17)32711-4