Two methods for assigning the α- and ε-dimethylamine nuclear magnetic resonance signals of a reductively 13C-methylated N-terminal lysine are described. One method utilizes the pH-induced selectivity of the reductive methylation reaction, and the other uses aminopeptidase to selectively remove the N-terminal lysine.
Roberson, K. J., Brady, P. N., Sweeney, M. M., Macnaughtan, M. A. Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins. J. Vis. Exp. (82), e50875, doi:10.3791/50875 (2013).