In this study, a cationic soluble peroxidase (POD) was homogeneously purified and biochemically characterized. The enzyme purification involved the combination of (NH 4 ) 2 SO 4 precipitation, CM-Sephadex cation exchange, and gel filtration chromatography. The purity of the enzyme was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, and one single prominent band was obtained with a molecular weight of approximately 45 kDa. The thermal and pH stability showed that the enzyme was stable at pH 5.0 and at 40°C, respectively. The activity remained stable at pH 4.0 at least for 10 days. K m and V max values were calculated from Lineweaver-Burk graph for each substrate. POD exhibited K m values of 0.0154 and 0.065 mM for guaiacol and H 2 O 2 , respectively. The enzyme was highly inhibited by sodium azide. This study could enrich the literature regarding the properties of POD from haricot bean that could be applicable to biomedical analysis. ARTICLE HISTORY

Cress (Lepidium sativum) is an annual herb from Brassicaceae family, and in some regions. It is known as peppergrass, garden cress, garden peppercress, pepperwort, or poor man's pepper. Cress is an important medicinal plant in some countries including Turkey. This plant has major scientific and therapeutic significance. Peroxidase (POD, E.C.1.11.1.7) is an oxidoreductase enzyme produced by a number of organisms. In this study, POD enzyme was purified from cress by ammonium sulphate precipitation, gel filtration, and CM-Sephadex ion-exchange chromatographies. K m and V max values were calculated from the Lineweaver-Burk graph for H 2 O 2 and guaiacol substrates and the substrate specificity of POD was investigated. The results showed that substrate specificity of H 2 O 2 is better than substrate specificity of guaiacol for this enzyme. The inhibition effects of three cations (Al 3+ , Cu 2+ , and Cr 3+) and one organic compound of cetyl trimethylammonium bromide were performed and their inhibition types were determined. Finally, optimum pH, optimum temperature, optimum ionic strength, and stable pH were determined.