Influence of Organic Acids on Kinetic Properties of Engineered <i>Phlebia radiata</i> MnP3 Enzymes (Wild-type and Mutants) during Mn (II) Oxidation

Abstract

Organic acids are potent inhibitors or activators of enzymes and are involved in the catalytic cycle of peroxidase. This study investigated the influence of some organic acids on kinetic parameters during the oxidation of Mn (II) catalyzed by recombinant Phlebia radiata wild-type and mutant manganese peroxidases. For the wild-type, the highest affinity (low Km) and highest catalytic efficiency were obtained in the presence of lactate. The E40H, E44H, D186H and D186N rPr-MnP3 variants exhibited similar characteristics as the wild-type with highest catalytic efficiencies in the presence of lactate. Michaelis constant, Km for rPr-MnP3 mutants was far higher compared to wild-type indicating that enzymes with less affinity for Mn (II) were created by mutation of the Mn (II)-binding site. This resulted in gross decrease in catalytic efficiencies of the mutants relative to wild-type. While D186H was least efficient in tartrate, D186N showed equivalent catalytic efficiencies in both malonate (0.31 mM-1s-1) and tartrate (0.30 mM-1s-1). E40H/E44H was most effective in the presence of malonate. Our outcomes agree with the hypothesis that certain organic acids are involved in the catalytic cycle of manganese peroxidase. We conclude that mutation specific preferences for organic acid chelators have been created and histidine is a better alternative to asparagine in retaining the activity of Mn peroxidase. For practical applications, tartrate is the most for wild-type, E40H, E44H, D186H and D186N activity while malonate is the best for E40H/E44H mutant. Creation of more mutants and investigation of specific modulators of these mutant enzymes are on-going in our laboratory.