The binding modes of fatty acid and peptide substrates that are catalyzed by hydrolase and aminopeptidase functions of the enzyme using same active site were compared. The overlay of two WT systems has given the overview of which parts of the active site were occupied by these two highly diverse substrates. Both the substrates bind perpendicular to each other occupying majorly the different portion of the active site and sharing the carboxylate recognition sites in common ( Figure 11A ). The long alkyl part of LTA4 was snuggly bound into the hydrophobic pocket formed by a mixture of aliphatic and aromatic residues including W311, F314, K364, L365, V367, Y378, and V381. The side chain of Cterminal Arg residue of RAR was fit into the small cavity formed by F356, Y378, S379, M564, K565, and R568 residues. The overlay of active site residues has shown very few structural changes between the WT systems of L-LTA4 and L-RAR systems including the side chain movements of Y378, Y383, and K565 residues ( Figure 11B ). The K565 residue was present in the loop in WT of L-LTA4 system and in the extended helix in WT of L-RAR system and thereby changing the flexibility and interacting behavior of K565. This adds explanation to the importance of K565 residue in assisting R563 residue in aligning the peptide substrate whereas this residue is not required in aligning fatty acid substrate.