Triplet-Triplet Energy Transfer in α -Trypsin

Experiments are reported that demonstrate that light absorbed by ionized tyrosinyl sensitizes the phosphorescence of tryptophanyl residues of native α -tripsin. The sensitization effect is abolished when α -tripsin is unfolded in guanidine hydrochloride. Under the experimental conditions used, the tryptophan phosphorescence could only have been induced by an electron-exchange interaction. These results, therefore, require that there be at least one ionized tyrosinyl-tryptophanyl pair in the native enzyme and that the distance between the two side chains be sufficiently short to permit electron exchange.