Abstract
Miswak is a chewing stick prepared from the roots, twigs or stems of Salvadora persica L. and widely used in Middle Eastern and Estern African cultures. Currently, its chemical components had antimicrobial and antioxidant activities. In the present study, peroxidase, as antioxidant and antibacterial enzyme, was screened in 4 parts of miswak and the level of peroxidase activity was recorded in the order of peel of stem > root without peel > peel of root > stem without peel. Generally, the people used the root without peel. By chromatography of miswak root without peel on DEAE-Spharose 3 peroxidases POI, POII and POIII were separated. Peroxidase POII with highest activity was reached to homogeneity by chromatography on Sephacryl S-200. The molecular weight of POII was found to be 70 kDa. o-Phenylenediamine was found to be the best substrate for the enzyme followed by guaiacol, o-dianisidine, pyrogallol and p-aminoantipyrine. The apparent Km for catalysis of H2O2 and guaiacol were 0.9 and 17.33 mM respectively. The enzyme had an optimum pH and temperature at 5.5 and 40 degrees C respectively. POII was stable at 10 to 40 degrees C and unstable above 50 degrees C. Most of the examined metal ions had partially inhibitory effects on POII, while Co2+, Fe3+ and Ca2+ were able to greatly enhance the activity. The metal chelators caused moderate inhibitory effects. The enzyme was highly inhibited by mercptoethanol, cysteine and ascorbic acid, while thiourea had moderate inhibitory effect. POII exhibited high resistance to protyolysis by trypsin. The highest storage stability at 4 degrees C was detected for POII in powder form compared to liquid form.