Methylation of guanine in vivo by the organophosphorus insecticide methamidophos.

The methylating capability of methamidophos, assayed by the formation of [7-14C]methylguanine in mouse liver, was investigated using a 14C-insecticide labelled at the O--CH3 group. Following i.p. administration of the toxicant, [7-14C]methylguanine could be isolated from liver nucleic acids of treated mice. The amount of 14C-label reached its maximum 6 h following administration of the insecticide. At maximum 14C-labelling, the amount of 7-methylguanine calculated as fraction of applied dose, was 20-22 X 10(-4) and 98-104 X -4, for DNA and RNA, respectively. The results obtained indicate also, that an appreciable amount of 14C-activity is incorporate via the C-1 pool.