Inhibition of Peroxidase-Catalyzed Oxidation of Chromogenic Substrates by Propyl Gallate and Its Polydisulfide

Abstract

Peroxidase-catalyzed oxidation of 2,2'-azino-di-(3-ethyl-2,3-dihydrobenzthiazoline-6-sulfonate) (ABTS) was competitively inhibited by propyl gallate (PG) and its polydisulfide (PGPDS) at 20 degrees C in 0.015 M phosphate-citrate buffer (pH 6.0). Under these conditions, the values of the inhibition constant (Ki) were equal to 62 and 5.6 microM, respectively, for PG and PGPDS. The stoichiometric inhibition factor (f; the number of radicals extinguished per molecule of an inhibitor) equaled 2.0 and 14.7, respectively, for PG and PGPDS. Peroxidase-catalyzed oxidation of o-phenylenediamine was barely affected by PG or PGPDS. PGPDS may be used as a stop-reagent of peroxidase-catalyzed ABTS oxidation, whereas PG may serve as a calibrating inhibitor in test systems for measurement of total antioxidant activity (in human biological fluids, natural preparations, juices, wines, and other objects).