Essential Oil of <em>Syzygium samarangense</em>; A Potent Antimicrobial and Inhibitor of Partially Purified and Characterized Extracellular Protease of </em>Escherichia coli</em> 25922

Volatile oils being secondary metabolites are phytoactive ingredients found in medicinal plants and may be active against various infectious microorganisms. The present study was carried out to evaluate the antimicrobial effect of the volatile oil from the leaf of Syzygium samarangense on Escherichia coli and its inhibition on the extracellular protease of this organism. The volatile oil inhibited the growth of Escherichia coli with IC50 of 0.42% (v/v). The extracellular protease of this organism exhibited highest activities at pH 7.0 and 43°C. This enzyme was moderately activated by the chloride salts of $Zn^{2+}, \>K^+$ and $Cu^{2+}$. The set of chloride salts of $Ba^{2+}, \>Pb^{2+}, \>Hg^{2+}$ and $Mg^ {2+}, \>Mn^{2+}, \>Co^{2+}, \>Ca^{2+}, \>Fe^{2+}$ were, respectively strong and mild inhibitors against the activity of this enzyme. The line weaver burke kinetic plot indicated a competitive mode of inhibition by the volatile oil on the enzyme with $V_{max}$ of $8.33×10^3\> μmol/min$ and the $K_m$ in the absence and presence of the volatile oil (inhibitor) were 0.23 mg/mL and 1.25 mg/mL, respectively. The highest percentage yield during purification was 66.3 and the highest purification fold was11.9 as compared to the crude enzyme. Sephadex G-100 gel filtration produced one peak each for total protein and enzyme activity. Therefore, the volatile oil from the leaf of Syzygium samarangense may possess antimicrobial activity and its inhibitory effect on the extracellular protease of Escherichia coli may be one of its modes of action on the pathogenic organisms.