DETECTION OF A REDUCED-FLAVIN TRIPLET-STATE IN FREE FLAVINS AND DNA PHOTOLYASE

A transient species was observed upon laser excitation (lambda(exc) = 355 nm) of reduced flavins (cFlH2) under anaerobic conditions. The tra nsient decayed with a lifetime of about 1 mus, was quenched by iodide ions and was assigned as the reduced flavin triplet state 3cFlH2. The triplet-state absorption spectrum assumed three forms, depending on th e pH of the solution, corresponding to 3cFlH2 and its monoprotonated a nd monodeprotonated forms. The triplet-state. lifetime was not sensiti ve to the presence of pyrimidine cyclobutane dimers, apparently ruling out its involvement in the dimer splitting reaction observed with mod el systems of reduced flavins. An analogous species is apparently form ed in the reduced form of Escherichia coli DNA photolyase.