title: On the mechanism and inhibition of DNA cytosine methyltransferases.
abstract: We have presented some data from studies of two different DNA cytosine methyltransferases. The first enzyme, M.Hha I, was shown to catalyze 3H exchange from poly(dG.[5-3H]dC), at a rate that is 7 to 10 times greater than the rate of methylation. The exchange is inhibited by AdoHcy in an uncompetitive fashion. This pattern of inhibition suggests an ordered reaction sequence for M.Hha I catalyzed methylation. The second enzyme, M.Hpa II, was demonstrated to make an irreversible adduct with azaC-DNA. The results provide evidence that both enzymes form covalent dihydropyrimidine intermediates during catalysis.
mesh_terms: D001483:Base Sequence; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D007700:Kinetics; D008745:Methylation; D011089:Polydeoxyribonucleotides; D012436:S-Adenosylmethionine / Q000378:metabolism; D013940:Thymidylate Synthase / Q000378:metabolism; D014316:Tritium
chemical_list: D011089:Polydeoxyribonucleotides; D014316:Tritium; D012436:S-Adenosylmethionine; D004248:DNA (Cytosine-5-)-Methyltransferases; D013940:Thymidylate Synthase; D003850:Deoxyribonuclease I