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''O''6-alkylguanine DNA alkyltransferase (also known as AGT, MGMT or AGAT) is a protein that in humans is encoded by the ''O''6-methylguanine DNA methyltransferase (''MGMT'') gene. O6-methylguanine DNA methyltransferase is crucial for genome stability. It repairs the naturally occurring mutagenic DNA lesion O6-methylguanine back to guanine and prevents mismatch and errors during DNA replication and transcription. Accordingly, loss of ''MGMT'' increases the carcinogenic risk in mice after exposure to alkylating agents. The two bacterial isozymes are Ada and Ogt. == Function and mechanism== Although alkylating mutagens preferentially modify the guanine base at the N7 position, ''O''6-alkyl-guanine is a major carcinogenic lesion in DNA. This DNA adduct is removed by the repair protein ''O''6-alkylguanine DNA alkyltransferase through an SN2 mechanism. This protein is not a true enzyme since it removes the alkyl group from the lesion in a stoichiometric reaction and the active enzyme is not regenerated after it is alkylated (referred to as suicide enzyme). The methyl-acceptor residue in the protein is a cysteine. ::Demethylation of 6-O-Methylguanosine to Guanosine 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「O-6-methylguanine-DNA methyltransferase」の詳細全文を読む スポンサード リンク
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