Specifically hydrolyzes both 8-oxo-deoxyguanosine triphosphate (8-oxo-dGTP) and 8-oxo-guanosine triphosphate (8-oxo-GTP) to the related monophosphates, thereby cleaning up the nucleotide pools and preventing misincorporation of 8-oxoGua into DNA and RNA (PubMed:1309939, PubMed:9311918, PubMed:15850400). It prevents replicational errors by removing an oxidatively damaged form of guanine (8-oxo-dGTP) from DNA and the nucleotide pool (PubMed:1309939). 8-oxo-dGTP can be inserted opposite dA and dC residues of template DNA with almost equal efficiency thus leading to A.T to G.C transversions (PubMed:1309939). MutT may also ensure transcriptional fidelity, removing 8-oxo-GTP from the ribonucleotide triphosphate pool (PubMed:9311918). However, due to the lower efficiency of RNA polymerase 8-oxo-GTP incorporation, MutT is probably not a major contributor to transcriptional fidelity (PubMed:25294823). It also hydrolyzes 8-oxo-dGDP and 8-oxo-GDP to their monophosphate form (PubMed:15850400). In vitro, can also use dGTP, dGDP and other various nucleoside di- and triphosphates, with much lower efficiency (PubMed:1851162, PubMed:1309939, PubMed:15850400, PubMed:23481913). Works cooperatively with MutM and MutY to prevent accumulation in the DNA of oxidized guanine residues (PubMed:7739614). 8-oxo-dGTP + H2O = 8-oxo-dGMP + diphosphate + H(+) 8-oxo-GTP + H2O = 8-oxo-GMP + diphosphate + H(+) 8-oxo-dGDP + H2O = 8-oxo-dGMP + H(+) + phosphate 8-oxo-GDP + H2O = 8-oxo-GMP + H(+) + phosphate kcat is 6.9 sec(-1) with 8-oxo-dGTP as substrate measured by the Fiske-SubbaRow assay. kcat is 5.5 sec(-1) with 8-oxo-dGTP as substrate measured by the Pi sensor assay. kcat is 11.2 sec(-1) with 8-oxo-GTP as substrate. Optimum pH is 9.0. Monomer. Disruption of the gene increases the rates of A:T to C:G transversion a thousandfold over the wild type level. Belongs to the Nudix hydrolase family.