Effect of methionine sulfoximine on methylation of guanine residues in astroglial transfer ribonucleic acids

Culture-grown astrocytes derived from 3-day-old rat brain were incubated in the presence of [3H]guanosine and of the convulsant agent L-methionine-dl-sulfoximine (MSO). The resulting [3H]tRNA was purified from control and MSO-exposed cells at several time points during the incubation and was hydrolyzed to [3H]guanine and four [3H]methyl guanines which were separated by high pressure liquid chromatography. Three of the four [3H]methyl guanines were more highly labeled in the [3H]tRNA of the MSO-exposed cells, relative to that of the control cells throughout the entire incubation period. The findings extend to cultured astrocytes, the stimulatory effect of MSO on the methylation of neural tRNA guanines, previously observed both in vitro using [14C]S-adenosyl-L-methionine and in vivo using [methyl-3H]L-methionine.