The oxidation of naphthalene sulfonate dyes by horse radish peroxidase

Horse radish peroxidase catalyses oxidation of ANS and TNS with hydrogen peroxide. TNS peroxidation may be followed fluorimetrically in the presence of as low as 10^?12m concentrations of the enzyme and permits determination of very low levels of peroxides. Initial rates of peroxidation of ANS and TNS confirmed the general mechanism of peroxidation by HRP. The second-order rate constants for the reduction of HRP compounds I and II were determined. Binding of the substrates to hydrophobic sites of bovine serum albumin or apoperoxidase rendered them inaccessible to the enzyme. While benzhydroxamic acid inhibited the oxidation of dianisidine, it exerted an activating effect on the peroxidation of naphthalene sulfonates. Due to the high reactivity of naphthalene sulfonates, their application as probes in biological systems containing possible traces of peroxidases and peroxides should be interpreted with great caution.