Imatinib is a clinically well-tolerated small molecule inhibitor that exerts selective, dual inhibition on the transforming growth factor beta and platelet-derived growth factor pathways. The recognition of an inactive conformation of Abl, in which a catalytically important Asp-Phe-Gly motif is flipped by approximately 180 degrees with respect to the active conformation, underlies the specificity of the cancer drug imatinib, which is used to treat chronic myelogenous leukemia. However, conformational analysis shows that the effect of the drug depends on the potential energy, which varies due to the alpha rotatable angles of the Abl tyrosine kinase domain. In this study, the author determines the change of binding energy between the Abl tyrosine kinase domain, due to the variation in rotatable angles, and bond lengthening. According to this study, the ratio between the required binding energy between the wild and mutated types is equal to 1: 1.16.