The histidine residue in the active centre of ribonuclease: II. The position of this residue in the primary protein chain

The carboxymethyl derivative of ribonuclease, obtained by the reaction of bromoacetic acid with the enzyme, has been oxidised and digested with chymo-trypsin. The peptides so formed have been separated by electrophoresis and chromatography and the peptide containing the introduced carboxymethyl group has been identified. This information locates the position in the protein chain of ribonuclease of the single histidine residue which reacts with bromoacetic acid, and hence locates at least a part of the active centre of this enzyme. The residue concerned is that histidine residue nearest to the C-terminal end of the protein chain (whose amino acid sequence is largely known). The result is considered in relation to other published evidence on primary structural requirements for ribonuclease activity. A start may be made on the task of constructing a model for the active centre of this enzyme.