This study has focused on structural changes and binding mode differences between wild types and mutant forms of hLTA4H-fatty acid and -tripeptide substrate complexes. Molecular dynamics (MD) simulations of two wild types of the enzyme-substrate complexes and three mutations including E272Q, R563A, and K565A were studied with LTA4 (fatty acid) and Arg-Ala-Arg (RAR, tripeptide) substrate ( Figure 2 ). The binding mode comparison of enzyme-substrate complexes revealed essential structural differences, which were not shown in X-ray structures, explaining the loss of catalytic functions of the enzyme. The overlay of binding modes of LTA4 and RAR substrates has proved the previous assumption of similar but overlapped active site is used in both the functions of the enzyme. The results from this study provide valuable information over the way the two functions of the enzyme are exerted over two substrates of diverse nature. In addition, the structural information obtained from this study can be utilized in structure-based hLTA4H inhibitor design as inhibition of the hydrolase and aminopeptidase functions will lead to the development of anticancer and anti-inflammatory drugs, respectively.