IMPROVED PEROXIDASE ASSAY METHOD USING LEUCO 2,3',6-TRICHLOROINDOPHENOL AND APPLICATION TO COMPARATIVE MEASUREMENTS OF PEROXIDATIC CATALYSIS

An improved peroxidatic assay method using leuco 2,3′,6-trichloroindophenol (leuco TIP) is described. TIP is conveniently reduced by sodium thiosulfate under standardized conditions. In contrast to leuco TIP prepared by hydrogen reduction methods, our substrate is stable at least 24 hours and the degree of reduction is completely reproducible. Under optimal conditions a linear relationship is found between peroxidase concentration and the rate of leuco TIP oxidation (ΔA657mμ/min). Autoxidation of substrate is negligible below pH 6. The leuco TIP method was useful in measuring activity of several peroxidatic catalysts ranging from ferrous ion with a relative activity of 1 to horseradish peroxidase with a relative activity of 2.8 × 107. © 1969.