Nuclear‐Magnetic‐Resonance‐Spectroscopic Studies of the Amino Groups of Insulin

Abstract

The amino groups of insulin have been studied by 1H and 13C nuclear magnetic resonance spectroscopy in insulin, zinc‐free insulin and methylated insulin. By difference spectroscopy it is possible to follow the shift with pH of the ɛ‐CH2 and δ‐CH2 proton resonances of lysine‐B29 in insulin. In methylated insulin the dimethyl proton resonances of glycine‐A1, phenylalanine‐B1 and lysine‐B29 can be followed as a function of pH. In native insulin pKapp values of 6.7 and 8.0 are obtained for phenylalanine‐B1 and glycine‐A1 (the assignment is tentative) and 11.2 for lysine‐B29. Separate resonances have been observed from the lysine‐B29 Nɛ‐(CH3)2 group for the monomeric and dimeric forms of methylated insulin, which indicates a small change in the environment of lysine‐B29 on dimerisation. The nuclear magnetic resonance spectral characteristics of these groups are, in general, consistent with the overall structure of the crystal form of the 2‐zinc insulin hexamer. Copyright © 1977, Wiley Blackwell. All rights reserved