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Inosine triphosphate pyrophosphatase is an enzyme that in humans is encoded by the ITPAgene,[5][6] by the rdgBgene in bacteria E.coli[7] and the HAM1gene in yeast S. cerevisiae;[8] the protein is also encoded by some RNA viruses of the Potyviridae family.[9] Two transcript variants encoding two different isoforms have been found for this gene. Also, at least two other transcript variants have been identified which are probably regulatory rather than protein-coding.[citation needed]
Function
The protein encoded by this gene hydrolyzes inosine triphosphate and deoxyinosine triphosphate to the monophosphate nucleotide and diphosphate.[6] The enzyme possesses a multiple substrate-specificity and acts on other nucleotides including xanthosine triphosphate and deoxyxanthosine triphosphate.[8] The encoded protein, which is a member of the HAM1 NTPase protein family, is found in the cytoplasm and acts as a homodimer.
Clinical significance
Defects in the encoded protein can result in inosine triphosphate pyrophosphorylase deficiency.[6] The enzyme ITPase dephosphorylates ribavirin triphosphate in vitro to ribavirin monophosphate, and ITPase reduced enzymatic activity present in 30 % of humans potentiates mutagenesis in hepatitis C virus.[10] Gene variants predicting reduced predicted ITPase activity have been associated with decreased risk of ribavirin-induced anemia, increased risk of thrombocytopenia, lower ribavirin concentrations, as well as a ribavirin-like reduced relapse risk following interferon-based therapy for hepatitis C virus (HCV) genotype 2 or 3 infection. [11]
Reading
Holmes SL, Turner BM, Hirschhorn K (1979). "Human inosine triphosphatase: catalytic properties and population studies". Clin. Chim. Acta. 97 (2–3): 143–53. doi:10.1016/0009-8981(79)90410-8. PMID487601.
Fraser JH, Meyers H, Henderson JF, et al. (1976). "Individual variation in inosine triphosphate accumulation in human erythrocytes". Clin. Biochem. 8 (6): 353–64. doi:10.1016/S0009-9120(75)93685-1. PMID1204209.
Clawson GA, Song YL, Schwartz AM, et al. (1992). "Interaction of human immunodeficiency virus type I Rev protein with nuclear scaffold nucleoside triphosphatase activity". Cell Growth Differ. 2 (11): 575–82. PMID1667585.
Marinaki AM, Duley JA, Arenas M, et al. (2005). "Mutation in the ITPA gene predicts intolerance to azathioprine". Nucleosides Nucleotides Nucleic Acids. 23 (8–9): 1393–7. doi:10.1081/NCN-200027639. PMID15571265. S2CID86308163.
Marinaki AM, Sumi S, Arenas M, et al. (2005). "Allele frequency of inosine triphosphate pyrophosphatase gene polymorphisms in a Japanese population". Nucleosides Nucleotides Nucleic Acids. 23 (8–9): 1399–401. doi:10.1081/NCN-200027641. PMID15571266. S2CID36126159.
Maeda T, Sumi S, Ueta A, et al. (2005). "Genetic basis of inosine triphosphate pyrophosphohydrolase deficiency in the Japanese population". Mol. Genet. Metab. 85 (4): 271–9. doi:10.1016/j.ymgme.2005.03.011. PMID15946879.
Atanasova S, Shipkova M, Svinarov D, et al. (2007). "Analysis of ITPA phenotype-genotype correlation in the Bulgarian population revealed a novel gene variant in exon 6". Therapeutic Drug Monitoring. 29 (1): 6–10. doi:10.1097/FTD.0b013e3180308554. PMID17304144. S2CID7286658.
