It has been inferred from DLTS measurements on electron-irradiated Si samples contaminated with copper and nickel that divacancies (V2) and vacancy-oxygen complexes (VO) are effective traps for mobile Cu and Ni interstitial atoms. Interactions of these impurities with VO and V2 result in the enhanced annealing out of the VO and V2 defects as well as in the formation of new electrically active centers. An enhanced annealing of the VO and V2 defects in Si:Cu crystals is accompanied by an appearance of electron traps with the energy levels at Ec - 0.60 eV and Ec - 0.17 eV. It is argued that these levels are related to acceptor levels of Cu-VO and Cu-V2 complexes. The stable configuration of the Cu-VO complex has been determined by means of quantum-chemical calculations. In Si:Ni crystals an energy level at Ec - 0.365 eV is related to a complex incorporating at least one Ni atom and a radiation-induced defect.