Cadmium Inhibition of a Structural Wheat Peroxidase

Abstract

The major peroxidase from 15-day-old wheat plants was purified to homogeneity by FPLC ion exchange and molecular exclusion chromatography. It consists of a single polypeptide of M₁ 37, 500 according to gel filtration and SDS-PAGE and has a pI of 7.0. Kinetics of pyrogallol peroxidation showed that the enzyme follows the accepted mechanism for peroxidase, with kinetic constants k₁= 4.4 × 10⁶ M^-1 s^-1 and k₃ = 8.6 × 10⁵ M^-1s^-1. The effect of different metal ions was assayed on peroxidase activity. None of the ions used had any effect on enzyme activity, except for Cd(II), which was an inhibitor. This was an unexpected and novel finding for a peroxidase. The kinetics of pyrogallol peroxidation at different concentrations of Cd(II) have been studied and a mechanism for Cd(II) inhibition proposed. The results obtained could explain, in part, cadmium-induced oxidative stress.

Key Words:

• Cadmium inhibition
• Kinetics
• Peroxidase
• Wheat