The interaction of ribonuclease with metal ions. I. Studies of cupric and zinc ions and the effect of cytidylic acid.

摘要: Abstract The interaction of ribonuclease A with cupric and zinc ions has been studied spectrophotometrically by potentiometric titration in the presence absence cytidylic acid derivatives. In acid, results suggest that each ion distributes among a set approximately four spectrally similar sites; site appears to consist mainly single imidazole side chain its adjacent peptide bond nitrogen atoms at neutral pH. No evidence for preferential chelation or between histidines-12 -119 found. 3'-cytidylate, binding both is strengthened. addition, spectrophotometric studies indicate ion-binding sites are altered 3'-cytidylate. These data compatible formation ternary complex ion, ribonuclease. By contrast, 2'-cytidylate does not alter type ligand which binds, but diminish very slightly affinity ion; these may compete one usually available ion. Several possible mechanisms inhibition suggested. include blocking active bound metal conformational changes induced elsewhere protein. importance cooperative interactions 3'-cytidylate particularly stressed as mechanism inhibition.