Direct study of alkylating agent--RNA interaction by 13C nuclear magnetic resonance spectroscopy.

The interactions of Torula yeast RNA with four biologically important methylating agents (methyl methanesulfonate, dimethyl sulfate, 1-methyl-1-nitrosourea, and 1-methyl-3-nitro-1-nitrosoguanidine) have been studied by 13C nuclear magnetic resonance spectroscopy. This direct stable isotope method eliminated all tedious and questionable degradation processes for determining the reactive sites and product distribution. Based on the integration curves, two types of product distribution can be distinctly observed according to the biological potency of the methylating agents [(a) weakly mutagenic and carcinogenic, methyl methanesulfonate and dimethyl sulfate and (b) strongly mutagenic and carcinogenic, 1-methyl-1-nitrosourea and 1-methyl-3-nitro-1-nitrosoguanidine]. With 90% 13C-enriched methylating agent, it significantly increases the specificity and sensitivity and provides better quantitative results.