We investigate the metal-insulator Mott transition in a generalized version of the periodic Anderson model, in which a band of itinerant non-interacting electrons is hybridrized with a narrow and strongly correlated band. Using dynamical mean-field theory, we show that the precondition for the Mott transition is that the total filling of the two bands takes an odd integer value. Unlike the conventional portrait of the Mott transition, this condition corresponds to a non-integer filling of the correlated band. For an integer constant occupation of the correlated orbitals the system remains a correlated metal at arbitrary large interaction strength. We picture the transition at a non-integer filling of the correlated orbital as the Mott localization of the singlet states between itinerant and strongly interacting electrons, having occupation of one per lattice site. We show that the Mott transition is of the first-order and we characterize the nature of the resulting insulating state with respect to relevant physical parameters, such as the charge-transfer energy.