Development of a radioimmunoassay for papain

Various well-tried radioimmunoassay (RIA) techniques were compared for the quantitation of papain. The evaluation of individual assays was performed by logit-log analysis. The most compatible analytical steps were combined in order to obtain the optimal analytical conditions of the assay. The preferred RIA involves papain labelling with lactoperoxidase, a double antibody method as the separation step and a 24 h incubation period at 2 degrees C. It permits the detection of 16 ng of papain per tube. In contrast, a method using immobilized antibody was satisfactory for rapid quantitation of papain with quite acceptable accuracy.