A COMPARISON BETWEEN THE HISTOCHEMICAL DEMONSTRATION OF NON-SPECIFIC ESTERASE ACTIVITY BY 5-BROMOINDOXYL ACETATE, α-NAPHTHYL ACETATE AND NAPHTHOL AS ACETATE

5-Bromoindoxyl acetate was used as a substrate for the histochemical demonstration of esterases. The pH optimum for this salt as used in this study was approximately 5. This differed from the optimum when α-naphthyl and naphthol AS acetates were used, which showed an optimum as determined by color reaction of between 7.3 and 8.4. This latter may be an artifact due to non-enzymatic hydrolysis. Naphthol binding may also vitiate the results. If these hydrolytic artifacts could be eliminated, the true optimum may be of a lower order. No hydrolysis or diffusion artifacts occur in any pH range with the 5-bromoindoxyl acetate. This may occur with the unsubstituted indoxyl acetate. The esterase reactions in various tissues following the use of 5-bromoindoxyl acetate was similar to the α-naphthyl and naphthol AS acetates with the exception of the large intestine which was negative with the 5-bromoindoxyl acetate. The reaction with 5-bromoindoxyl acetate was enhanced by taurocholate in the pancreas and inhibited in the kidney, liver and intestine. This seems to indicate that 5-bromoindoxyl acetate is hydrolyzed by both lipases and esterases from the data of this study. Because of the fine and uniform granularity of the resulting 5,5' dibromoindigo crystals, this substrate should be valuable in the study of esterases.