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Invited Review Enzymes Involved in Purine Metabolism

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Invited Review Enzymes Involved in Purine Metabolism Histol Histopathol (1999) 14: 1321-1340 Histology and 001: 10.14670/HH-14.1321 Histopathology http://www.hh.um.es From Cell Biology to Tissue Engineering Invited Review Enzymes involved in purine metabolism - A review of histochemical localization and functional implications Y. Moriwaki, T. Yamamoto and K. Higashino Third Department of Internal Medicine, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan Summary. Many enzymes are involved in the reactive oxygen species, while the extensive tissue biosynthesis, interconversion, and degradation of purine localization of xanthine dehydrogenase/oxidase suggests compounds. The exact function of these enzymes is still several other roles for this enzyme, including a unknown, but they seem to play important roles other protective barrier against bacterial infection by than in purine metabolism. To elucidate their functional producing either superoxide radicals or uric acid. roles, it is imperative to clarify their tissue distribution at Furthermore, an involvement in cellular proliferation the cellular or subcellular level. The present review and differentiation has been suggested. Urate oxidase is summarizes the currently available information about generally considered a liver-specific enzyme, except for their histochemical localization and proposed functions. bovines which possess this enzyme in the kidney. Urate In general, 5' -nucleotidase has been considered as a oxidase is exclusively located in the peroxisomes of fish, marker enzyme for the plasma membrane, and is frogs, and rats, but was lost in birds, some reptiles, and considered to be a key enzyme in the generation of primates during evolution. A histochemical demon­ adenosine, a potential vasodilator. However, from its stration of allantoin-degrading enzymes has not been wide range of localization in tissues it is also considered performed, but these enzymes have been located in to be related to the membrane movement of cells in the peroxisomes by sucrose density gradient centrifugation. transitional epithelium, cellular motile response, AMP deaminase activity is higher in skeletal muscle transport process, cellular growth, synthesis of fibrous than in any other tissues. AMP deaminase may be protein and calcification, lymphocyte activation, involved in a number of physiological processes, such as neurotransmission, and oxygen sensing mechanism. the conversion of adenine nucleotide to inosine or Adenosine deaminase (ADA) is present in all tissues in guanine nucleotide, stabilizing the adenyl ate energy mammals. Although the main function of ADA is the charge, and the reaction of the purine nucleotide cycle. development of the immune system in humans, it seems There are three distinct isozymes (A, B, C) with different to be associated with the differentiation of epithelial kinetic, physical, and immunological properties. cells and monocytes, neurotransmission, and mainte­ Isozymes A, B, C have been isolated from muscle, liver nance of gestation. Purine nucleoside phosphorylase (kidney), and heart tissue, respectively. In the muscle, (PNP) is generally considered as a cytosolic enzyme, but AMP deaminase isozymes exist in a different part, recently, mitochondrial PNP, a different protein from suggesting a multiple functional role of this enzyme. cytosolic PNP, was reported. PNP is also widely High hypoxanthine-guanine phosphoribosyltransferase expressed in human tissues. It is found in most tissues of (HGPRT) activity is found in some regions of a normal the body, but the highest activity is in peripheral blood adult human brain. However, very little is known granulocyte and lymphoid tissues. It is also related to the regarding the histochemical tissue localization of development of T-cell immunity in humans as is ADA. HGPRT. Immunohistochemical localization of its Moreover, its contribution to centriole replication and/or developmental expression suggests that HGPRT may not regulation of microtubule assembly has been suggested. be essential for purine nucleotide supplement in the Immunohistochemical localization of xanthine oxidase segmentation of brain cells, but may playa significant has been reported in various tissues from various animal role in the developing hippocampus. species. Xanthine oxidase has been suggested to be involved in the pathogenesis of post-ischemic Key words: Purine metabolism-related enzymes, Tissue reperfusion tissue injury through the generation of distribution, Histochemistry, Function Offprint requests to: Yuji Moriwaki, M.D., Third Department of Internal Medicine, Hyogo College of Medicine, Mukogawa·cho 1-1, Nishinomiya, Introduction Hyogo 663·8501 , Japan. Fax: 81 -798-45·6474. e-mail: tetsuya@hyo­ med.ac.jp There are two major pathways in purine ribo- 1322 Enzymes of the purine metabolism nucleotide biosynthesis and degradation (Fig. 1). One is adenylosuccinate synthetase, and adenylosuccinate lyase de novo purine synthesis, and the other is the purine (Goodman and Lowenstein, 1977). AMP is recycled to reutilizing pathway by which purine bases and IMP by the reaction of AMP deaminase. De­ nucleosides are salvaged to respective ribonucleotides. phosphorylation of AMP, IMP, xanthosine mono­ The pathway of de novo purine synthesis consists of 11 phosphate (XMP), and guanosine monophosphate enzymatic reactions, forming inosine monophosphate (GMP) is catalyzed by purine 5' -nucleotidase and (IMP) (Wyngaarden and Kelley, 1976). As the initial nonspecific phosphatases to adenosine, inosine, step, PRPP (5'-phosphoribosyl I-pyrophosphate) xanthosine, and guanosine (Fox, 1978). Adenosine is synthetase produces PRPP, a key substrate in de novo further degraded to inosine by adenosine deaminase purine synthesis (Wyngaarden and Kelley, 1976; Becker (ADA). Purine nucleoside phosphorylase (PNP) mainly and Kim, 1987), from Mg-adenosine triphosphate (ATP) cleaves the nucleosides inosine and guanosine to and ribose 5-phosphate. Then, amidophosphoribosyl­ hypoxanthine and guanine, respectively. The oxidation transferase catalyzes the condensation of PRPP with L­ of hypoxanthine to xanthine, and subsequently to uric glutamine to generate phosphoribosylamine. The acid, is catalyzed by xanthine oxidase. In humans and succeeding reactions in the de novo pathway are directed primates, uric acid is the end product of purine to the construction and closure of the purine ring (Palella catabolism. In lower vertebrates, however, uric acid and Fox, 1989). All synthesized purine compounds are further undergoes degradation to allantoin, allantoate, ultimately derived from inosine monophosphate (IMP). ureidoglycollate, urea, and finally NH3, by urate Three enzymes are involved in the purine nucleotide oxidase, allantoinase, allantoicase, ureidoglycollate cycle: adenosine monophosphate (AMP) deaminase, lyase, and urease, respectively. The purine salvage ~ - ~ -I phosphoribosylamine 1-~ PRPP synthetase ATase GAR synthetase ~GAR transformytase IC-A'R 1- EJ - ~ - FGAR SAleM , AIR AIR synthetase FGAM synthetase synthetase carboxytase I S-AICAR I-I AICAR I-I FAICAR I AS lyase AK:AR transformytase f IMP cyclohydrolase IMP dehydrogenase GMP synthetase ~ - IAMP.s f- ~- ~-~ AS lyase AS synthetase f f AK t S'-ND S'-ND S'-ND • ,-------, ' ADA Fig. 1. Pathways in purine ribonucleotide biosynthesis, interconversion, and degradation. Abbreviations: ATase, amidophosphoribosyl­ transferase; AK, adenosine kinase; APRT, adenine phosphoribosyltransferase; HGPRT, hypoxanthine­ guanine phosphoribosyltransferase; S'-ND, S' ­ nucleotidase; ADA, adenosine deaminase; PNP, purine nucleoside phosphorylase; XO , xanthine oxidase; R-S-P, ribose-S-phosphate; PRPP, S'­ phosphoribosyl 1-pyrophosphate; GAR, S'- phospho­ ribosylglycineamide; FGAR, S'-phosphoribosyl N­ formylglycineamide; FGAM, S'-phosphoribosyl N­ formylglycineamidine; AIR, S'-phosphoribosyl-S­ aminoimidazole; C-AIR , S'-phosphoribosyl-S-amino-4- imidazole carboxylate; S-AICAR, S'-phosphoriboyl-S­ amino-4-imidazole·succinocarboxamide; AICAR, S'­ phosphoribosyl-S-amino-4-imidazolecarboxamide; FAICAR, S'-phosphoribosyl-S-formamido-4-imidazole­ carboxamide; IMP, inosine monophosphate; AMP, , ur ••s. adenosine monophosphate; AMP-S, adenylo­ succinate; XMP , xanthosine monophosphate; GMP, ~ guanosine monophosphate. 1323 Enzymes of the purine metabolism pathway involves hypoxanthine-guanine phospho­ method because of its lower nonspecific precipitate ribosyltransferase (HGPRT) which salvages hypo­ (Blok et aI., 1982; Robinson and Kamovsky, 1983). By xanthine and guanine to IMP, and adenine phosphoribo­ an enzyme-histochemical method using the cerium ion syltransferase (APRT) which salvages adenine to AMP technique, 5' -nucleotidase activity has been found on the (Wyngaarden and Kelley, 1976; Arnold, 1978). plasma membrane of all bladder transitional epithelial In recent years, some of the enzymes involved in cells, including the free surface of superficial cells, purine metabolism, especially in purine nucleotide suggesting that 5' -nucleotidase present on the luminal interconversion and catabolism, have been extensively surface of superficial cells plays a special role in the investigated with regard to their structures, substrate membrane movement of these cells in the transitional specificities, tissue and subcellular localization/ epithelium by accelerating actin polymerization (Zhang expression, molecular cloning, and regulation. Enzymes et aI., 1991). 5'-nucleotidase activity has also been involved in purine metabolism play an important role in shown in murine peritoneal resident macrophage
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