ABSTRACT
Photochemical reaction dynamics of the primary events in recombinant bacteriorhodopsin (bRrec) was studied by femtosecond laser absorption spectroscopy with 25-fs time resolution. bRrec was produced in an Escherichia coli expression system. Since bRrec was prepared in a DMPC-CHAPS micelle system in the monomeric form, its comparison with trimeric and monomeric forms of the native bacteriorhodopsin (bRtrim and bRmon, respectively) was carried out. We found that bRrec intermediate I (excited state of bR) was formed in the range of 100 fs, as in the case of bRtrim and bRmon. Further processes, namely the decay of the excited state I and the formation of intermediates J and K of bRrec, occurred more slowly compared to bRtrim, but similarly to bRmon. The lifetime of intermediate I, judging from the signal of ΔAESA(470-480 nm), was 0.68 ps (78%) and 4.4 ps (22%) for bRrec, 0.52 ps (73%) and 1.7 ps (27%) for bRmon, and 0.45 ps (90%) and 1.75 ps (10%) for bRtrim. The formation time of intermediate K, judging from the signal of ΔAGSA(625-635 nm), was 13.5 ps for bRrec, 9.8 ps for bRmon, and 4.3 ps for bRtrim. In addition, there was a decrease in the photoreaction efficiency of bRrec and bRmon as seen by a decrease in absorbance in the differential spectrum of the intermediate K by ~14%. Since photochemical properties of bRrec are similar to those of the monomeric form of the native protein, bRrec and its mutants can be considered as a basis for further studies of the mechanism of bacteriorhodopsin functioning.