1H NMR parameters of the N‐terminal 13‐residue C‐peptide of ribonuclease in aqueous solution

Abstract

The ¹H NMR chemical shifts and the spin‐spin coupling constants of the non‐exchangeable protons of the N‐terminal 13‐residue C‐peptide of ribonuclease A, obtained by cleavage of the enzyme with cyanogen bromide, have been measured in a 5 mM solution in D₂O (pH 3.0, 24°C) at 360 MHz. The titration parameters for end groups (Lys‐1 and homo‐Ser‐13) and side chains (Lys‐1, Glu‐2, Lys‐7, Glu‐9 and His‐12) have been determined. The chemical shifts, their temperature coefficients and the vicinal coupling constants, ³J(HNCH‐α), for the exchangeable NH protons have been measured in a 5 mM solution in D₂O/H₂O (1:9 v/v) at pH 3.0. An assignment of observed signals to individual residue protons based on characteristic shifts, standard double resonance experiments, spectral simulations and titration shifts is proposed. All experimental evidence indicates that under the conditions studied the C‐peptide is in a random coil form.