Effect of Mercuric Chloride on Kinetic Properties of Horseradish Peroxidase

Mercury is one of the three major environmental metal poisons, and mercuric chloride is a highly reactive compound whi ch can harm cells by a variety of mechanisms including direct inte racti on with sulphydryl groups of proteins and enzymes, therefore affecting the enzymatic activity . Th is study focused on the effec t of Hg ++ on hor seradi sh peroxidase (donor: hydrogen peroxide oxidoreductase, EC 1.11.1.7) (HRP) (Isoenzym e C) activ ity. In the presence of 88 rnM hydrogen peroxid e Km for o-dianisidine oxidation was 0.05 millimolar and Vmax was 8.5 mo M.S square -1. Incubation of the enzyme with I to 100 millimolar mercuric chlor ide for 5-20- and 60 min resulted in pro gressive inhib ition of the en zymat ic ac tiv ity. At low Hg++ concentrations the inhibition was reversible by exce ss substrate, whil e at high Hg++ concentrat ion the inhibition was not reve rsible. Results also indicated that the type of inhibition depended on the duration of incub ation of the enzyme with metal ion and on the Hg++ concentration. So we could conclude that the type of inhibition changed from noncompetitive to mix with increased incub at ion time and increased metal concentration.