X-ray film digestion: a semi-quantitative assay for proteolytic enzymes used in immunohaematology

A simple semi-quantitative assay method for proteolytic enzyme solutions used in blood group serology is described. The method is an adaptation of a technique formerly used for assay of faecal trypsin and is based on the digestion of the gelatin coating of unexposed X-ray film. A Spearman rank correlation coefficient of 0.8 was obtained when the X-ray film technique was compared with a spectrophotometric method using azoalbumin as substrate. The method is not suitable as a reference technique or as a substitute for serological control, but is useful for monitoring or comparing enzyme preparations in some circumstances or situations.