Proton magnetic resonance studies on ribonuclease T1

The chemical shifts of the C-2 protons of the histidine residues of ribonuclease T₁ (RNase T₁) have been studied as a function of pH in ²H₂O. The results are interpreted in terms of interactions of the histidine residues with carboxylate anions of acidic amino acid residues.The presence of histidines in the active site of the enzyme is indicated by changes, which occur in their C-2-PMR-absorption region on the addition of guanosine, 2′ GMP, and 3′-GMP. One of the three histidines interacts with the phosphate group of 3′-GMP. The differences in the PMR-spectra of the RNase T₁-3¹-GMP and RNase T₁-2′-GMP complexes suggest that these nucleotides are bound to the enzyme differently.