## 3 Results
### Effects of Metal Ions, Inhibitors, and Surfactants on the Bacterial Pectinase  
The effects of metal ions, inhibitors, and surfactants on pectinase activities are presented in Figure 6. The purified pectinase was almost completely inhibited by 5 mM of Hg\({}^{2+}\), Cd\({}^{2+}\), EDTA, SDS, and \(\beta\)-mercaptoethanolhanol. The inhibitory effect of Hg\({}^{2+}\) and Cd\({}^{2+}\) on pectinase activity may be due to different and diverse functional groups present in the active site with which the metal ions interact and, thus, inactivate the enzyme. Hg\({}^{2+}\) ions have been found to have the ability to bind to thiol groups in enzymes, and this leads to the complete loss of enzyme activity [42]. Cd\({}^{2+}\) imposes its inactivating effect not by causing apparent structural changes in enzymes, but by binding sites occupation [43] or displacing metal ions from the active center [44]. No significant enzymatic inhibition or activation was detected by Cu\({}^{2+}\), Co\({}^{2+}\), Fe\({}^{2+}\), Mn\({}^{2+}\), and Zn\({}^{2+}\). A slight activation effect on the purified pectinase was observed in the presence of 5 mM Ca\({}^{2+}\) and Mg\({}^{2+}\). Similar results were reported for the polygalacturonase isolated from _Bacillus subtilis_ C4, which was also activated by Ca\({}^{2+}\) and Mg\({}^{2+}\)[45]. [PERSON] et al. (2010) [46] commented on metal ions such as Ca\({}^{2+}\) and Mg\({}^{2+}\) that might play a vital role in maintaining the active confirmations of the alkaline pectinase and alkaline endo polygalacturonase to stimulate the activity. In contrast, no effect of enzyme activation by Ca\({}^{2+}\), Fe\({}^{2+}\), or Mg\({}^{2+}\) was found for the pectinase from _Bacillus subtilis_ 15A-B92 [1].  
The stability of the enzyme against surfactants is one of the important parameters allowing enzymes to be used in various types of industries. In this study, the pectinase activity was weakly stimulated by Tween-20 and Tween-80, whereas SDS, EDTA, andmercaptoethanol completely inhibited pectinase activity. [PERSON] et al. (2012) [47] purified a polygalacturonase that was stimulated by Tween-20 and Tween-80. The same stimulatory effect of pectinase from _Bacillus subtilis_ strain Btk27 was also reported by [PERSON] and [PERSON] (2017) [27]. However, some authors have reported a weak inhibition of pectinase activity by the surfactants Tween 20 and 80 [1]. SDS also inhibited a thermo-alkaline pectinase enzyme from _Hyloceneus polyrhizus_ isolated by [PERSON] et al. (2014) [48]. The stimulatory effect of some surfactants is probably due to the fact that they can improve the contact frequency between the active site of the enzyme and the substrate by lowering the surface tension of the aqueous medium [49].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Substrate, (1\%)** & **Enzyme Activity (U/mg)** & **Relative Activity (\%)** \\ \hline Polygalacturonic acid & 132 & 100 \(\pm\) 1.7 \\ \hline Citrus pectin & 102 & 77 \(\pm\) 1.0 \\ \hline Apple pectin & 99 & 75 \(\pm\) 1.3 \\ \hline Xylan & 19.8 & 15 \(\pm\) 1.0 \\ \hline Galactose & 10 & 7.5 \(\pm\) 1.5 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Substrate specificity of pectinase from _V. salarius_ strain 434.