Peroxidase

This chapter reviews the principle, measurement, and the preparation of peroxidase (POD). POD occurs in plants and in certain animal cells. The enzyme catalyses the oxidation of many organic compounds by hydrogen peroxide such as amines (o-phenylenediamine), p-phenylenediamine, benzidine, phenols, and hydroquinone. Ascorbic acid can also act as a hydrogen donor in conjunction with other oxidizable compounds such as o-toluidine, as can mixtures of phenols and amines. The specificity of peroxidase for peroxides is high. Only H2O2, methyl and ethyl hydroperoxides combine with peroxidase. On the other hand, the specificity of the peroxidasehydroperoxide complex for the organic compounds mentioned is low. A comparison of the activity of peroxidases of different origin is difficult if different substrates are used. To measure the peroxidase activity the oxidation product or the unchanged substrate is determined chemically or spectrophotometrically at different reaction times. It should be noted that, in the absence of peroxidase, the oxidation of certain organic compounds can be catalysed by H2O2 and traces of heavy metals. The methods employing p-phenylenediamine and guaiacol have proved successful even with turbid enzyme solutions.