1H n.m.r. parameters of the N‐terminal 19‐residue S‐peptide of ribonuclease in aqueous solution

Abstract

The 1H NMR chemical shifts and the spin-spin coupling constants of the N-terminal 19-residue S-peptide of RNase A were measured in a 10 mM solution in D2O, pD 3.0, 27.degree. C, at 300 MHz. The titration parameters for end groups Lys-1 and Ala-19 and side chains Lys-1, Glu-2, Lys-7, Glu-9, Arg-10, His-12 and Asp-14 were determined at 90 MHz. An assignment of observed signals to individual residue protons based upon characteristic shifts, spectral analysis, double resonance, titration shifts and comparison with the spectrum of C-peptide (N-terminal 13-residue) is proposed. Differences in the observed chemical shifts, pKa''s and titration shifts with reference to those proposed as random coil parameters are not large enough to assume the existence of a significant population of secondary structure in the conditions studied. The H.alpha. chemical shifts differences can be accounted for by the Phe-8 phenyl ring current for an extended peptide backbone conformation and appropriate values for the torsion angles .chi.1 Phe-8 and .chi.2 Phe-8.