Kinetics of the reaction of compound III of horseradish peroxidase with hydrogen peroxide and NADPH

The kinetic study of the reaction of Compound III of horseradish peroxidase with reduced nicotinamide adenine dinucleotide phosphate (NADPH) was investigated in phosphate buffer as a function of ionic strength at 25 °C. Two successive reactions involving increase and decrease in absorbance with time were observed. Each reaction was first order with respect to the concentration of horseradish peroxidase. The observed rate constants were ionic strength dependent within the range of 0.06 – 0.30 M. The logarithmic values of the rate constants against the square root of the ionic strength showed that both NADPH and Compound III of horseradish peroxidase are of same ionic charges in the first reaction but different ionic charges in the secondreaction.Key words: Ionic strength, rate constant, horseradish peroxidase, NADPH