title: In vivo assay for somatic point mutations induced by genotoxic carcinogens: incorporation of [35S]methionine into a rat liver cytochrome b5 normally lacking sulphur-containing amino acids.
abstract: The trypsin fragments of rat liver microsomal cytochrome b5 (Tb5) lack both methionine (met) and cysteine (cys), i.e., the sulphur-containing amino acids. Tb5 should therefore contain no 35S-radioactivity after isolation from animals treated with [35S]met or [35S]cys. If, however, the nucleic acids coding for this polypeptide have been damaged by a genotoxic carcinogen, a miscoding could result in an incorporation of met or cys into the polypeptide so that Tb5 could now be 35S-radiolabelled. Two experiments are described, the first one where a toxic regimen of N-nitrosomorpholine (NNM) to rats resulted in a significant increase of 35S-radioactivity in the Tb5 of liver microsomes, and a second experiment with a non-toxic regimen of N,N-diethylnitrosamine (DENA), where no increase was observable.
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D003573:Cytochrome b Group / Q000235:genetics*; D015786:Cytochromes b5; D004052:Diethylnitrosamine / Q000633:toxicity; D007700:Kinetics; D008297:Male; D008715:Methionine / Q000378:metabolism*; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009152:Mutagenicity Tests / Q000379:methods; D009153:Mutagens; D009154:Mutation; D009602:Nitrosamines / Q000633:toxicity*; D010446:Peptide Fragments / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D013462:Sulfur Radioisotopes; D014357:Trypsin
chemical_list: D002273:Carcinogens; D003573:Cytochrome b Group; D009153:Mutagens; D009602:Nitrosamines; D010446:Peptide Fragments; D013462:Sulfur Radioisotopes; D004052:Diethylnitrosamine; C002741:N-nitrosomorpholine; D015786:Cytochromes b5; D008715:Methionine; D014357:Trypsin