Physicochemical studies of human O6-methylguanine-DNA methyltransferase.
O6-Methylguanine-DNA methyltransferase, present in most organisms, removes mutagenic and carcinogenic O6-alkylguanine from DNA by accepting the alkyl group in a stoichiometric reaction. The protein has been partially purified from human placenta. It reacts with second-order rate constants of 2.20 x 10(8) and 0.067 x 10(8) lmol-1 min-1 at 37 degrees C for duplex and single-stranded DNA substrates, respectively. The corresponding value for the alkylated base in synthetic poly(dC, dG, m6dG) is 0.02 x 10(8) l mol-1 min-1. The native protein is monomeric with a molecular mass of 22-24 kDa. Methylation of the protein does not lead to a gross change in its conformation but causes a slight reduction in its isoelectric point of 6.2. Although DNA protects the protein from heat inactivation, both duplex and single-stranded DNAs inhibit its activity in a concentration-dependent manner. The transferase reaction rate is also strongly inhibited by salt with about 20% of the maximum rate observed in physiological ionic strength. This inhibition is nonspecific with respect to the ions of univalent salts.
Bhattacharyya
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University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences.
Foote
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Boulden
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Mitra
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D000818:Animals; D002417:Cattle; D002482:Cellulose / Q000031:analogs & derivatives / Q000737:chemistry; D004247:DNA / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D006367:HeLa Cells / Q000201:enzymology; D006801:Humans; D007526:Isoelectric Point; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000302:isolation & purification; D008970:Molecular Weight; D019853:O(6)-Methylguanine-DNA Methyltransferase; D010920:Placenta / Q000201:enzymology; D051381:Rats; D011916:Rats, Inbred F344
C033190:DNA-cellulose; D002482:Cellulose; D004247:DNA; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase