CMR studies of protein modification. Progressive decrease in charge density at the epsilon-amino function of lysine with increasing methyl substitution.

Progressive methyl substitution at the ε-amino group of lysine results in a progressive downfield shift of the signals from the ε and $\text{N}$-methyl carbon atoms in the Carbon-13 nmr spectra of the resulting ε-$\text{N}$-methylated lysine derivatives. The results are consistent with the view that the greater the number of ε,$\text{N}$-methyl groups on protein basic aminoacid residues, the greater the affinity of these residues for anionic species, e.g. as in histone-DNA interactions.