The aim of this thesis consisted in the identification of key amino acids residues governing the transition from active to inactive protein kinase domain conformation. We used the kinase domain of c-Src as a case study because of the wealth of structural information on this protein. We could demonstrate that residues governing the kinase domain dynamics of c-Src are located far from the ATP-binding site and form a network of hydrophobic interactions at the interface between the N-lobe and the C-lobe of the kinase domain. The identified amino acids and in particular Leu317 dictate the conformational plasticity of the kinase domain by influencing the rate of the DFG-flip. Furthermore, we could provide experimental evidence that the DFG-flip is the most probable molecular mechanism for the release of ADP at the end of the catalytic cycle and that both DFG-in and DFG-out conformations are present within the catalytic cycle of c-Src.