Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

O6-Methylguanine-DNA methyltransferase, a DNA repair enzyme which transfers the methyl group of O6-methylguanine residue to a cysteinyl residue in the methyltransferase itself, was examined in rat organs by quantifying the S-methylcysteine formed in the methyl acceptor protein. Among the various organs examined, the spleen exhibited the highest enzyme specific activity followed by the thymus, liver, lung and testis. Brain had the lowest activity. The patterns of subcellular distribution of the methyltransferase in spleen and liver were different: while 75-80% of the activity was present in the nuclear fraction of the spleen, 54% of the activity in the liver was found in the nuclei and 35% in the cytosolic fraction. Forty-five and thirty-five percent of the total nuclear enzyme activity could be extracted with 1 M and 2 M NaCl solutions, respectively, indicating that the repair enzyme is not tightly bound to the nuclear matrix. When isolated nuclei were incubated with [methyl-3H]DNA substrate and subsequently fractionated into histone and non-histone protein fractions, over 90% of the radioactivity was coeluted on a Bio-Rex 70 column with the non-histone fraction and only a negligible amount of radioactivity was found to be associated with the histone fraction. The molecular mass of the [methyl-3H]methyltransferase in the non-histone fraction was determined to be 23,000, and its pI value was found to be 6.6 by two-dimensional polyacrylamide gel electrophoresis.
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PMID:Studies on the distribution of O6-methylguanine-DNA methyltransferase in rat. 394 77

Human lymphoid cell lines contain a DNA repair enzyme which removes the mutagenic alkylation lesion O6-methylguanine from DNA. The enzyme transfers the methyl group to a protein cysteine residue, generating S-methylcysteine, and is inactivated as a consequence of the reaction. Apparently the methylated enzyme represents a dead-end complex. The transfer reaction is very rapid and is completed in less than 1 min at 37 degrees, but methyl group transfer from single-stranded DNA or heavily damaged DNA is less efficient. The active methyltransferase and the methylated protein both have molecular weights of 21,000 to 22,000, as determined by gel filtration. Lymphoid cell lines proficient in repair of O6-methylguanine in vivo, Mex+, contain 10,000 to 25,000 molecules of the methyltransferase per cell. In contrast, repair-deficient cell lines, Mex-, do not contain detectable amounts of the enzyme. The latter point was verified by applying a partial purification procedure for the enzyme to cell-free extracts from two Mex- cell lines.
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PMID:O6-Methylguanine-DNA methyltransferase of human lymphoid cells: structural and kinetic properties and absence in repair-deficient cells. 634 62