The distance between the most important metal (Zn 2+ ) ion and oxygen atom of the epoxy ring in case of L-LTA4 systems is very important for the hydrolase function of the enzyme. The average distance value observed in WT system (0.56 nm) was lower compared to the mutant systems. Among mutant systems R563A system has shown the higher average distance value of 0.78 nm whereas E271Q and K565A systems have shown similar average distance value of 0.69 nm and 0.63 nm, respectively. During the end of the simulations, this distance in E271Q and K565A systems has reduced close to the distance of WT but R563A has maintained higher distance until the end ( Figure 5A ). In terms of L-RAR systems, the distance between the same metal ion and carbonyl oxygen atom of N-terminal peptide bond was measured and compared between the L-RAR WT and mutant systems. As observed in L-LTA4 systems, WT of L-RAR systems has maintained the lower average distance value of 0.59 nm whereas Figure 5B ). The hydrogen bonds formed between the protein and bound ligands were also calculated for all the systems under study to investigate the molecular interactions that are lost during the mutations. In L-LTA4 systems, WT system has formed high number of average hydrogen bonds (5.7) compared to the mutant systems. The K565A system has shown an average number of hydrogen bonds of 5.0 whereas E271Q and R563A systems have formed only 1.7 and 1.8 average number of hydrogen bonds with the bound ligand ( Figure 6A ). This reduced number of hydrogen bonds correlate well with previously reported loss of hydrolase activity of the enzyme in E271Q and R563A mutated systems [14, 45] . In terms of L-RAR systems, the E271Q system has formed more number of average hydrogen bonds (8.7) with the bound RAR. Whereas the WT system has shown an average hydrogen bond value of 8.0, the other mutant systems R563A and K565A have shown the average hydrogen bond values of 4.3 and 3.9, respectively ( Figure 6B ). This result of number of hydrogen bond values observed between protein and RAR has proved the importance of both R564 and K565 to maintain the substrate alignment in the active site and the binding strength of the substrate. But the high number of observed hydrogen bonds in E271Q system does not correlate with the observed loss of catalytic activity due to the mutation of E271. This indicated that other structural disturbances script the loss of catalytic function of the enzyme.