Proton‐Magnetic‐Resonance Studies of Complexes of Pancreatic Ribonuclease A with Pyrimidine and Purine Nucleotides

Abstract

In continuation of earlier work new results on the behaviour of certain proton resonances of pancreatic ribonuclease A and of nucleotides during complex formation are reported. By varying the structure of the base or the position of the phosphate group at the ribose moiety it can be shown that the main structural feature of the ribonuclease · pyrimidine‐nucleotide complexes is maintained. However, the microscopic binding constants of the interactions of the various parts of a nucleotide with the corresponding amino acid sidegroups are different for nearly all the investigated complexes. While the modified purine base of 8‐oxoadenosine 3′‐phosphate seems to be bound in the pyrimidine binding site of ribonuclease A also, the base of the other adenosine nucleotides studied occupy other sites at the enzyme. For adenosine 3′‐ and 5′‐monophosphate this might be the binding site shown to be specific for purine bases by X‐ray crystallography. But the results obtained for the ribonuclease · adenosine‐2′‐phosphate complex suggest that the adenosine nucleotides do not bind exclusively in this purine binding site.