IDENTIFICATION AND OBSERVATION OF ALKYL PROTON RESONANCES OF THE AMINO‐TERMINAL RESIDUES OF BOVINE NEUROPHYSINS

Publisher Website
Google Scholar
Abstract
Analysis of the 220 MHz proton magnetic resonance spectra of bovine neurophysins-I and -II and of the effects of pH and succinylation on these spectra has allowed identification of the -CH3 proton resonances of the amino-terminal alanine of both proteins and of the -CH3 resonance of methionine-2 of neurophysin-II. The alanine -CH3 resonance of neurophysin-I is a sharp doublet at all pH values between 1 and 10.5 indicating relatively few restrictions on its mobility. By contrast, the -CH3 resonances of the amino-terminal alanine and methionine-2 of neurophysin-II undergo pH-dependent changes in broadening compatible with the formation of an intramolecular salt-bridge at neutral pH between the protonated α-amino and an unprotonated side chain carboxyl. The results suggest that differences in the properties of the two proteins are partially mediated by conformational differences involving their amino-terminal sequences. The potential usefulness of the amino-terminal resonances as n.m.r. ‘reporter’ signals is additionally demonstrated by studies of the effects of spin labels on the neurophysin-I amino-terminal alanine resonance; these studies place the amino-terminus of neurophysin-I approximately 14 Å from residue 3 of peptides bound to the strong neurophysin hormone-binding site.