## 4 Discussion  
We performed an analysis of published data on the known techniques for cultivating _E. coli_ cells for producing His\({}_{6}\)-OPH. Based on these data, the total His\({}_{6}\)-OPH activity per liter of culture medium was evaluated for each case summarized in Table 4.  
Comparison of the results of various studies has shown that addition of PFCs to the culture medium allows for accumulating the maximum total His\({}_{6}\)-OPH activity per 1 L of medium. Note that cultivating _E. coli_ cells for producing His\({}_{6}\)-OPH under conditions used previously resulted [34] in some cases to the accumulation of greater biomass or higher His\({}_{6}\)-OPH activity of the cells as compared to the data obtained in present study. However, only the addition of PFH and polyether II allowed for increasing the specific rate of cell growth, His\({}_{6}\)-OPH activity of the cells and the concentration of accumulated biomass in the medium. Thus, the combination of these effects resulted in the maximum increase of the total His\({}_{6}\)-OPH activity per 1 L of the culture medium, so the overall efficiency of cell cultivation process improved.  
As compared to the productivity of the various processes of His\({}_{6}\)-OPH, accumulation has shown that the addition of 1% (\(v/v\)) of polyether II ensures maximizing of this parameter. However the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline _E. coli_ Strain & \begin{tabular}{c} **Yield of Biomass** \\ **(CDW/L)** \\ \end{tabular} & \begin{tabular}{c} **A\({}_{\text{max}}\)* in the Cells** \\ **(U/g)** \\ \end{tabular} & \
\begin{tabular}{c} **Process** \\ **Productivity** \\ **(U/L/h)** \\ \end{tabular} &
\begin{tabular}{c} **Total His\({}_{6}\)-OPH** \\ **Activity (U/L)** \\ \end{tabular} \\ \hline DH5a [33] & 2.8 & 130 & 17.3 & 364.0 \\
5.8 & 44 & 12.2 & 255.2 \\ \hline W3110 [34] & 2.7 & 38 & 5.1 & 102.6 \\ \hline SG13009[pREP4] [34] & 4.3 & 34 & 6.1 & 146.2 \\ \hline SG13009[pREP4] & 3.7 & 88 & 13.6 & 325.6 \\ (this work) & 5.1 & 91.5 & 19.3 & 463.5 \\ (this work) & 4.4 & 93.3 & 17.1 & 410.7 \\ \hline \hline \end{tabular}  
* A\({}_{\text{max}}\) is the maximum His\({}_{6}\)-OPH activity of the cells obtained upon cultivation, a Conditions reported previously [33]; b Addition of 1% (\(v/v\)) of polyether II; c Addition of 0.5% (\(v/v\)) of PFH.  
\end{table}
Table 4: Basic characteristics of various techniques for producing His\({}_{6}\)-OPH.  
Figure 4: The electrophoregram conducted under non-denaturing (**a**) (1—without PFH addition, 2—with PFH addition) and denaturing (**b**) conditions (1–3 without PFH addition, 4–6 with PFH addition, the 1,4—total protein fractions; 2,5—insoluble protein fractions, 3,6—soluble fraction), reflecting the impact of the presence of PFH in the culture medium on the biosynthesis of OPH. M—markers of molecular weight.  
productivity of cells in present of polyether II was slightly higher that the same parameter obtained by adding PFH to the culture medium (Table 4).  
Additionally, taking in to account the high price of polyether II as reagent for biotechnology processes, we certainly should recommend the application of PFH for the use in production of His\({}_{6}\)-OPH in _E. coli_ SG13009[pREP4] cell.