Related Experiment Videos
Protein bound carboxyl-methyl ester as a precursor of methanol formation during oxidation of dimethylnitrosamine in
1Fels Research Institute, Temple University School of Medicine, Philadelphia, Pa 19140.
Abstract:
Protein modification with dimethylnitrosamine was studied in vitro in the presence of hamster liver microsomal fraction. Incorporation of radioactive methyl groups from dimethylnitrosamine into the exogenously added protein was dependent on the microsomal mixed function oxidase system. The methylation yielded chemically labile and stable products. The former was completely hydrolyzed by the mild alkaline treatment, pH 7.4, 100 degrees C, for 5 min and the hydrolytic product was identified as methanol indicating that the activated methyl groups from dimethylnitrosamine were incorporated into a protein as a carboxyl-methyl ester. Thus, it is suggested that methanol, recovered as one of the products during the biodegradation of dimethylnitrosamine [8], is derived, at least in part, from protein carboxyl-methyl ester which is unstable under physiological conditions.
Insights
Dimethylnitrosamine activates methyl groups to modify proteins via a liver enzyme system. This process forms unstable protein carboxyl-methyl esters, which can yield methanol under physiological conditions.
Area of Science:
- Biochemistry
- Toxicology
- Molecular Biology
Background:
- Dimethylnitrosamine is a known toxic compound.
- Protein modification can alter cellular function.
- Microsomal enzymes play a role in xenobiotic metabolism.
Purpose of the Study:
- To investigate the in vitro mechanism of protein modification by dimethylnitrosamine.
- To identify the products of dimethylnitrosamine-induced protein methylation.
- To elucidate the role of the microsomal mixed function oxidase system in this process.
Main Methods:
- In vitro study using hamster liver microsomal fraction.
- Incubation with radioactive dimethylnitrosamine and exogenous protein.
- Analysis of methylated protein products using alkaline hydrolysis.
- Identification of hydrolysis products via chemical analysis.
Main Results:
- Dimethylnitrosamine methylation of protein occurred in vitro, dependent on the microsomal mixed function oxidase system.
- Methylation produced both labile and stable products.
- Labile products were hydrolyzed to methanol, indicating protein carboxyl-methyl ester formation.
- Protein carboxyl-methyl ester is unstable under physiological conditions.
Conclusions:
- Activated methyl groups from dimethylnitrosamine can be incorporated into proteins as carboxyl-methyl esters.
- This protein-bound methanol can be released under physiological conditions.
- This pathway may contribute to methanol formation during dimethylnitrosamine biodegradation.