The streptococcus faecalis oxidases for reduced diphosphopyridine nucleotide : VI. Inhibition of the flavoprotein peroxidase by its electron donor

Abstract

When the flavorprotein, DPNH peroxidase, is incubated with DPNH, enzyme activity slowly decays with first-order kinetics o k = 0.066 min −1, pH 5.4). The cosubstrate, hydrogen peroxide, can prevent but cannot reverse the inhibition. The kinetics of the inactivation were investigated and shown to be consistent with the following mechanisms. (a) DPNH combines with the enzyme to form a binary complex that is kinetically active and has a characteristic absorption spectrum. (b) In the absence of peroxide, the complex is slowly and irreversibly converted to an inactive form. (c) Hydrogen peroxide prevents the inhibition by combining with the binary complex to form a ternary complex that dissociates into products. The ternary complex is not inactivated except at very high DPNH concentrations; this type if inactivation is rever.