High resistance of the order of 10⁸ Ω•cm in semi-insulator GaAs crystals, both in clean undoped and in intentionally doped samples, is associated with deep electron traps. The intrinsic EL2 defects are the most known such electron centers. Interaction of electron centers with ligand nuclei combined with spin diffusion produces an effective route of nuclear spin-lattice relaxation in solids. The character of this interaction specifies the rate and evolution with temperature of the contribution of electron centers to total spin-lattice relaxation of host nuclei.