Theoretical investigation on the electron transfer between tryptophan and tyrosine has been performed at the level of HF/6-31G and GASSCF/6-31G. The solvent effect has been considered by means of the conductorlike screening model. After geometric optimizations of the isolated donor and acceptor, inner reorganization energy and reaction energy difference of the electron transfer have been obtained. For comparison, the ionization potentials are calculated for tryptophan and tyrosine employing Koopmans' theorem and CASSCF/6-31G method respectively. The transition energy from the ground state to the lowest excited state of these two amino acids is also calculated. Theoretical results give good explanations on the experimental phenomena that N_3~· can preferably oxide the side chain of tryptophan residue and then the electron transfer from tyrosine residue to tryptophan residue follows in peptides involving tryptophan and tyrosine.

Key words: CHARGE TRANSFER REACTION, OXIDATION REDUCTION REACTION, TRYPTOPHAN, TYROSINE, CONFIGURATION, TRANSITION