Inhibition assays of horseradish peroxidase by hexavalent chromium and other heavy metals

In this study, individual and combinations of heavy metals were tested at different pH for their inhibition potential by horseradish peroxidase (HRP). At pH of 6.4, maximum velocities for a single substrate concentration of hydrogen peroxide was observed. The double reciprocal of Lineweaver-Burk plot gave the same values ofK(m)and decreasedV(max)represents the non-competitive type of inhibition by hexavalent chromium metal ions. The IC(10)value of Cr(6+)ion for free HRP was achieved at 0.55ppm, while inhibition for 1ppm of substrate concentration was 24.5%. For other tested heavy metals, no significant inhibition properties were observed except for Cd(2+)and Mg(2+)metal ions. However, when combined with Cr(6+)ions, substantial changes were detected. Based on IC(10)values, the sensitivity order for free HRP for individual metal ions was observed as Cd2+> Cr6+> Mg2+> Cu2+> Cr3+> Mn(2+)while the combination with Cr(6+)gave the order as Cd2+> Cu2+> Cr3+> Cr6+> Mg2+> Mn2+. The order of inhibition byquaternary combinations of metal ion were in the order (Cr6++ Cd2++ Cu2++ Cr3+) > (Cr6++ Cu2++ Mg2++ Cd2+) >= (Cr6++ Cd2++ Mg2++ Cr3+) >= (Cr6++ Cu2++ Mg2++ Cr3+), while the quinary combination (Cr6++ Cr3++ Cu2++ Mg2++ Cd2+) was the most effective grouping. The studies shown excellent selectivity towards Cr(6+)and suggest further use of HRP enzymes in the design and selection of biosensors for heavy metals and other pollutants.

Automated summary

In this study, the inhibition potential of heavy metals on horseradish peroxidase at different pH levels was investigated. The results showed significant variations in the inhibition potential of different heavy metal ions, with substantial changes observed when combined with Cr(6+) ions.