Characterization of O6-methylguanine-DNA-methyltransferase (O6-MGMT) activity in Xiphophorus fishes

Ronald B. Walter, Huang Mo Sung, Gabe W. Intano, Christi A. Walter

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8 Citations (Scopus)


We utilized a custom-synthesized double-strand oligonucleotide containing a single O6-methylguanine (O6-MG) residue within a restriction endonuclease recognition site to determine O6-methylguanine-DNA-methyltransferase (O6-MGMT) activity in various tissue extracts prepared from Xiphophorus fish. The results suggest Xiphophorus fish O6-MGMT activity has many of the same characteristics as Escherichia coli and mammalian O6-MGMT's including rapid reaction kinetics consistent with stoichiometric removal of methyl groups, but exhibits a temperature optimum of 23°C. Results from protein extract activity assays indicate O6-MGMT activity patterns among four Xiphophorus tissues followed the order: brain ≥ testes > gill ≥ liver. In mammals, O6-MGMT activity is high in liver, while activity in brain is minimal (i.e. ≈9% of liver); however, we report that in the Xiphophorus fishes examined, brain tissue extracts exhibited much higher (≈six-fold) O6-MGMT activity levels than liver. Comparison of O6-MGMT activity between Xiphophorus species employed in tumor induction experiments did not indicate significant differences in ability to clear the pre-mutagenic O6-MG from the oligonucleotide substrate.

Original languageEnglish
Pages (from-to)11-22
Number of pages12
JournalMutation Research - Genetic Toxicology and Environmental Mutagenesis
Issue number1-2
Publication statusPublished - 2001 Jun 27

All Science Journal Classification (ASJC) codes

  • Genetics
  • Health, Toxicology and Mutagenesis


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