The reaction of 2′(3′)-0-bromoacetyluridine with ribonuclease A

Reaction of bovine pancreatic ribonuclease A with 2′(3′)-0-bromoacetyluridine at pH 5.5, 25°C, leads to a rapid and stereospecific inactivation of the enzyme with formation of 3-carboxymethylhistidine-12 RNase A and 1-carboxymethylhistidine-119 RNase A in the ratio of 7:1. The product distribution is the reverse of that obtained for the reaction of bromoacetate with RNase A. The results suggest that the imidazole group of histidine-12 is favorably disposed to interact with the phosphate residues of cyclic nucleotide substrates and 2′- and 3′-nucleotide inhibitors.