title: Modification of a specific tyrosine residue of ribonuclease A with a diazonium inhibitor analog.
abstract: The diazonium salt of 5'-(4-aminophenyl phosphoryl)-uridine 2'(3')-phosphate reacts stoichiometrically with pancreatic ribonuclease and modifies only one tyrosyl residue, which was identified as Tyr 73 in the amino acid sequence. The modification does not inhibit the biological activity of RNAase on ribonucleic acid, although a large change in the binding constant towards cytidine cyclic phosphate was observed. The modification can be inhibited by addition of the competitive inhibitor cytidine 2'(3')5'-diphosphate and may indicate that Tyr 73 is the most exposed residue or has a unique reactivity towards this reactive substrate analog.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D003979:Diazonium Compounds; D007700:Kinetics; D010179:Pancreas / Q000201:enzymology; D012260:Ribonucleases / Q000037:antagonists & inhibitors; D013053:Spectrophotometry; D014443:Tyrosine; D014500:Uracil Nucleotides
chemical_list: D000596:Amino Acids; D003979:Diazonium Compounds; D014500:Uracil Nucleotides; D014443:Tyrosine; D012260:Ribonucleases