COMPARISON OF THE TIME-RESOLVED ABSORPTION AND PHOSPHORESCENCE FROM THE TRYPTOPHAN TRIPLET-STATE IN PROTEINS IN SOLUTION

Measurement of the room temperature Trp triplet state lifetime in prot eins by time-resolved phosphorescence can provide valuable information on the structure and dynamics of proteins in solution. Our time-resol ved absorption measurements on the long-lived states resulting from el ectronic excitation of the chromophore demonstrate the presence of mor e complex behavior than revealed by time-resolved phosphorescence. To provide additional insight into this behavior, a comparative study of time-resolved transient absorption and time-resolved phosphorescence o f proteins in solution was carried out. The results show that the time evolution of the long-lived states observed through transient absorpt ion often differs considerably from that observed in time-resolved pho sphorescence. In some proteins, the presence of competing reactions co mplicates the interpretation of the transient absorption measurements (which may affect the phosphorescence yield). A more complete characte rization of these processes will likely prove useful in the study of p rotein structure and dynamics in solution.