## 3 Results and Discussion
### Molecular Docking  
The experimental results were supplemented with molecular-docking analysis using MOE. Experimental results suggested that the binding site for ETB binding on BSA to be Site I (subdomain IIA) and Site III (subdomain IIB) [26; 42] (Figure 6A,B). Blind docking in silico was performed for the BSA-ETB system, and the results of the binary system were compared to the ternary-system docking for the BSA-ETB in the presence of RUT, NAR,  
Figure 5: Ultraviolet-visible spectra for (**A**): BSA (1.5 \(\upmu\)M) in presence and absence of ETB (0.00–10 \(\upmu\)M) and in presence of (**B**): RUT; (**C**): NAR; (**D**): SIN. and SIN. It was observed that ETB binds to subdomain IIA and subdomain IB of BSA in corroboration with previous studies. The molecular docking results are presented in Table 4 and suggest high binding energy for the BSA-ETB system at subdomain IIA. The binding energy showed a decline in the presence of all the flavonoids RUT, NAR, and SIN, with the highest value of reduction in the binding energy in RUT, followed by SIN and then NAR. Thus, the presence of the three drugs RUT, NAR, and SIN influenced the binding energy of ETB with BSA. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Complex**} & \multirow{2}{*}{**Ligand**} & \multicolumn{3}{c}{**Recceptor**} & \multirow{2}{*}{**Interaction**} & \multirow{2}{*}{**Distance**} & \multirow{2}{*}{**Score**} & \multirow{2}{*}{**Kcal mol\({}^{-1}\)**} & \multirow{2}{*}{**Subdomain**} \\ \cline{3-3} \cline{5-8}  & \(n33\) & CD & ARG & \(217\) & (A) & H-acceptor & \(3.39\) & \\ \cline{2-8}  & \(6\)-ring & NE & ARG & \(256\) & (A) & pi-cation & \(3.8\) & \\ \hline \multirow{2}{*}{ETB(BSA-NRN)} & O14 & OG & SER & \(286\) & (A) & H-donor & \(3.14\) & \\ \cline{2-8}  & O1 & NE & ARG & \(217\) & (A) & H-acceptor & \(3.04\) & \\ \hline \multirow{2}{*}{ETB(BSA-RTN)} & N38 & OD2 & ASP & \(450\) & (A) & H-donor & \(3.18\) & \\ \cline{2-8}  & N33 & CE & LYS & \(439\) & (A) & H-acceptor & \(3.51\) & \\ \hline \multirow{2}{*}{ETB(BSA-SPA)} & C29 & \(5\)-ring & HIS & \(287\) & (A) & H-pi & \(4.15\) & \\ \cline{2-8}  & \(6\)-ring & CD & ARG & \(194\) & (A) & pi-H & \(3.15\) & \(-7.428\) \\ \cline{2-8}  & \(6\)-ring & NH1 & ARG & \(198\) & (A) & pi-cation & \(4.31\) & \\ \hline ETB-BSA & N33 & CA & TYR & \(137\) & (A) & H-acceptor & \(3.49\) & \(-7.495\) \\ \hline \multirow{2}{*}{ETB(BSA-NRN)} & O28 & NE & ARG & \(427\) & (A) & H-acceptor & \(3.21\) & \\ \cline{2-8}  & \(6\)-ring & CD & PRO & \(110\) & (A) & pi-H & \(4.53\) & \\ \hline \multirow{2}{*}{ETB(BSA-RTN)} & O5 & NZ & LYS & \(114\) & (A) & H-acceptor & \(2.87\) & \\ \cline{2-8}  & O28 & NH1 & ARG & \(185\) & (A) & H-acceptor & \(3.13\) & \(-7.272\) & IB \\ \cline{2-8}  & O28 & NH2 & ARG & \(185\) & (A) & H-acceptor & \(2.97\) & \\ \hline \multirow{2}{*}{ETB(BSA-SPA)} & O5 & NH2 & ARG & \(185\) & (A) & H-acceptor & \(2.93\) & \\ \cline{2-8}  & \(6\)-ring & N & LEU & \(115\) & (A) & pi-H & \(4.41\) & \\ \cline{2-8}  & \(6\)-ring & CB & ARG & \(144\) & (A) & pi-H & \(4.22\) & \\ \cline{2-8}  & \(6\)-ring & CD & ARG & \(144\) & (A) & pi-H & \(4.04\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Molecular-locking results for the binary and ternary BSA-ETB systems. Figure 6: Two-dimensional molecular-docking conformation for BSA ETB system (**A**): Site I and (**B**): Site III. Further, the comparison was made in the binding energies at subdomain IB, and it was observed that the binding energies for the BSA-ETB system in the presence of RUT, NAR, and SIN were lower than the BSA-ETB system in their absence, as shown in Table 4.  
The amino acids Glu291, Leu218, Glu152, Arg198, Arg256, Arg217, Ser286, Leu237, Leu259, Ile289, Tyr149, Ile263, Ala290, Trp213, Ala260, Val240, and Arg194 in the vicinity of the ETB at the binding site in subdomain IIA surrounded the binding pocket at subdomain IB with amino acids Lys 116, Pro117, Leu115, Ile181, Leu122, Glu182, Tyr137, Lys136, Arg185, Ile141, Tyr160, Val188, Glu140, Asp118, and Thr121.