Guanine and 7-methylguanine amino proton exchange rates as a function of buffer pK: implications for the exchange mechanism.

Using the stopped-flow kinetic method we have measured the deuteration rate of the amino protons in 2'deoxyguanosine 5'monophosphate and 7-methylguanosine 5'monophosphate. For both compounds the exchange rates are accelerated with increasing concentration of a large number of buffers with widely differing pKs. The results obtained, in conjunction with a theoretical model study, give rise to serious doubts concerning the normally accepted mechanism of amino proton exchange involving a pre-protonation at N7.