Study of triple-singlet energy transfer in an enzyme-dye complex using optical detection of magnetic resonance.

We have made optical detection of magnetic resonance (ODMR) measurements on the enzyme alpha-chymotrypsin, as well as on its complex with the dye, proflavin. Evidence that triplet-singlet energy transfer occurs in the complex is provided by the observation of characteristic tryptophan ODMR signals while monitoring the delayed fluorescence of the dye. The luminescence decay kinetics of the complex indicates that nontrivial triplet-singlet transfer originates from several (at least three) tryptophan residues of the enzyme. ODMR sensitivity can be enhanced by coupling the sublevels of a weakly radiative triplet state to a fluorescent dye which satisfies Förster's (Förster, T. (1948), Ann. Phys. (Leipzig) 2, 55; (1965), in Modern Quantum Chemistry, Istanbul Lectures, Part III, Sinanoglu, O., Ed., New York, N.Y., Academic Press, p 93) conditions for energy transfer.