RESUMEN
A complete normal coordinate analysis of morphine using Wilson's GF matrix method and Urey Bradley force field has been carried out to understand the dynamical behaviour of morphine in relation to Leu5- and Met5-enkephalins. In addition, charge distribution on different atoms of morphine, along with that of Leu5- and Met5-enkephalins using CNDO/2 method is also reported. The similarity in charge distribution on some of the sites of these molecules is indicative of the possible interactions at the same receptor site. It is surmised that the recognition and interaction of active sites with the receptor must be dynamical in nature and for this the modes involving the active sites should play an important role. It is found that the binding to receptors is not static, but a dynamic process.