Protein fluorescence, dynamics and function: exploration of analogy between electronically excited and biocatalytic transition states.

With the advent and development of time-resolved spectroscopic techniques and substantial progress in understanding of photophysical and photochemical phenomena, a new goal may be achieved: modeling of biochemical reaction or its elementary step by a photochemical event occurring within the probe, bound to a protein molecule. The probe may be located in a well-determined site of the protein matrix and report on the modulation of the reaction rate by the matrix and by the surrounding solvent, or by interactions in multiprotein complexes and in biomembranes. The advantages of this approach are obvious: in contrast to ordinary biochemical reaction, the excited-state reaction may be started by a short light pulse, and its kinetics may be observed directly with high resolution in time. In addition, if the reaction rate is influenced by the dynamics of the protein matrix, these dynamics may be studied simultaneously with the reaction, by using the same or a similar probe and within the same time range. In this review, the prospects for application of probes exhibiting electron transfer, proton transfer, molecular rotations and isomerizations are presented and discussed. The general problem of photochemical modeling of biochemical reactions is discussed. This modeling may result in deeper understanding of enzyme catalyzed reaction mechanisms.