[Isolation of neutral proteinase of ribosomes (cathepsin R)]

A method for isolation of cathepsin R from rat liver ribosomes allowing for a 264-fold increase of specific activity is described. The purification procedure includes enzyme extraction from ribosomes with 2-4 M LiCl and two-step affinity chromatography on Sepharose with immobilized soy bean trypsin inhibitor and trypsin-Sepharose.