## 3 Results
### Molecular Docking Study
Moreover, the interaction of QL and the ACE involved the formation of four H-bonds, including Ala356 (2.0 A; 2.1 A), Glu411 (2.9 A), and Arg522 (2.4 A), and no \(\pi\)-\(\pi\) binding was detected. However, Glu411 and Arg522 are well known for their ability to bind to zinc ions and are important ligands to the second Cl\({}^{-}\) of ACE, respectively. The appearance of these essential residues in the QL-ACE complex may \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**tACE Residues Involved in**} & \multicolumn{6}{c}{**No. of H-Bonds and Corresponding Distance (Å)**} \\ \cline{2-7}  & **WLQL** & **LPSW** & **WL** & **QL** & **LP** & **SW** \\ \hline Arg522: O & 2; 2; 2.2 & 1.9; 2.1 & \(-\) & 2.4 & \(-\) & 2.1; 2.5 \\ Glu384: H & 2.2; 2.4 & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ Glu384: O & \(-\) & \(-\) & 3.3 & \(-\) & \(-\) & \(-\) \\ Glu384: N & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & 3.7 \\ Asn70: H & \(-\) & \(-\) & \(2.0\) & \(-\) & \(-\) & \(-\) \\ Glu411: O & \(-\) & \(-\) & \(-\) & 2.9 & 3 & \(-\) \\ Ala356: OH & \(-\) & \(-\) & \(-\) & \(2;2.1\) & \(1.7;1.9\) & \(-\) \\ Glu123: NH & \(-\) & \(2;2.7\) & \(-\) & \(-\) & \(-\) & \(-\) \\ Tyr360: H & \(-\) & \(2.2;2.2\) & \(-\) & \(-\) & \(-\) & \(-\) \\ Ala354: H & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & 1.9 \\ His353: H & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & 2.2 \\ Tyr523: O & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & 2.2 \\ Total & 5 & 6 & 2 & 4 & 3 & 6 \\ \hline \hline \end{tabular}  
* The residue number of tACE (PBD code: 108A).
* H-bond position: donor or receptor atoms. Repeated residues indicate formation of two separate H-bonds by the same amino acid.  
\end{table} 
Table 4: Hydrogen bonds observed between the top-ranked docked poses of peptides and tACE *. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sequences**} & \multirow{2}{*}{**Potential Binding Site**} & **Total Binding Sites** & **Number of H-Bonds** & **Number of Pi-Pi** & **CDOCKER** \\ \hline WLQL & Tyr523, Arg522, Glu384, His383 & 9 & 5 & 4 & 80.4321 \\ LPSW & Tyr360, Lys118, Glu123, Arg522 & 8 & 6 & 2 & 55.1801 \\ WL & Glu384, Asn70 & 2 & 2 & 0 & 58.8494 \\ QL & Arg522, Ala356, Glu411 & 4 & 4 & 0 & 62.3901 \\ LP & Trp357, Ala356, Glu411 & 4 & 3 & 1 & 53.3389 \\ SW & Glu384, His353, Tyr523, Arg522, & 10 & 6 & 4 & 61.9276 \\ His387, His410, Ala354 & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Potential binding sites of ACE inhibitory peptides based on molecular docking analysis. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**tACE Residues Involved in**} & \multicolumn{6}{c}{**No. of Pi-pi Bonds and Corresponding Distance (Å)**} \\ \cline{2-7}  & **WLQL** & **LPSW** & **WL** & **QL** & **LP** & **SW** \\ \hline Tyr523: H & 5; 6.3 & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ His383: H & 4; 4.3 & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ Arg522: H & \(-\) & 6.8 & \(-\) & \(-\) & \(-\) & \(-\) \\ Lys118: H & \(-\) & 6.8 & \(-\) & \(-\) & \(-\) & \(-\) \\ Trp357: H & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ His387: H & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(4.4;5.4\) \\ His410: H & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(4.2;4.7\) \\ \hline Total & 4 & 2 & 0 & 0 & 1 & 4 \\ \hline \hline \end{tabular}  
* The residue number of tACE (PBD code: 108A).
* H-bond position: donor or receptor atoms. Repeated residues indicate formation of two separate H-bonds by the same amino acid.  
\end{table} 
Table 5: Pi-pi bonds observed between the top-ranked docked poses of peptides and tACE *. explain the enhanced ACE inhibitory activity after the pre-incubation experiment. This peptide showed the CDocker energy of \(-\)62.3901 kJ/mol. The tetrapeptide LPSW only interacted with the ACE receptor via the second binding sites that contained Arg522, Lys118, and Tyr360 Glu123. Binding bonds were formed in this LPSW-ACE complex, including two \(\pi\)-\(\pi\) interactions with Arg522 (6.8 A); Lys118 (6.8 A), and six hydrogen bonds with Tyr360 (2.2 A; 2.2 A); Glu123 (2.0 A;2.7 A) and Arg522 (1.9 A; 2.1 A).