title: Some evidence suggesting the existence of P2 and B3 sites in the active site of bovine pancreatic ribonuclease A.
abstract: In order to clarify the subsite structure of ribonuclease A (RNase A), the interactions of pdTp, pAp, dTpdAp, and pdTpdAp with RNase A were investigated by means of kinetic studies and 31P NMR spectroscopy. The pH profile of the 31P NMR spectrum of RNase A-pdTp complex indicated the interaction of the 3'- and 5'-phosphates with RNase A. The signal of 3'-phosphate of pdTp in the presence of RNase A gave a characteristic titration curve indicating the participation of more than 2 ionic groups in the P1 subsite. A similar 31P NMR titration was observed in the case of 5'-phosphate of pAp in the presence of RNase A. The results indicated that pAp interacted with RNase A at the P1, B2, and P2 sites. dTpdAp and pdTpdAp inhibited RNase A action more markedly than dTpdA, indicating the contribution of 3'- and 5'-terminal phosphate groups attached to dTpdA to the affinity of RNase A. The 31P NMR spectra of RNase A-dTpdAp and pdTpdAp complexes excluded the possible interaction of the monoester type phosphate of the inhibitors with the P1 site of RNase A, thus indicating the binding of the 3'-side phosphates with the P2 subsite of RNase A.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011742:Pyrimidine Nucleotides / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D011742:Pyrimidine Nucleotides; D011743:Pyrimidines; D012259:Ribonuclease, Pancreatic