Contribution of E-amino groups to ninhydrin color production in proteins.

The ninhydrin color given by model compounds and by characterized proteins shows a consistent contribution from the epsilon-amino group of lysine of about 67 percent of that of an alpha-amino group, except in free lysine or in N-terminal lysine, where the epsilon-amino group makes a small contribution (7 to 10 percent) to the total color. This information can be applied to structure determination of N(epsilon) peptides of lysine.