Investigations into the dynamics and mechanisms of ultrafast photoinduced reactions taking place in photoresponsive protein nanospaces (PINS)

摘要

In this article, we discuss mainly our recent results of femtosecond (fs) fluorescence dynamics studies, together with some previous important investigations on ultrafast photoinduced reactions in protein nanospaces (PNS) of various photoresponsive proteins, such as the photoactive yellow protein (PYP), its site-directed mutants, PYP analogues with modified chromophores, rhodopsin (Rh) for vision, and also several flavoproteins (FP). Based on these studies, the effects of the PNS on the dynamics and mechanisms of the ultrafast and hilghly efficient photoreactions of these proteins have been elucidated. In the early stage of our fluorescence dynamics studies of PYP, we found faster initial decays at the blue and red edges of the spectrum and no dynamic Stokes shift, which we ascribed to a slight narrowing of the fluorescence band shape at the early stage of the decay, due to the damping of coherent vibrations coupled with the photoinduced twisting of the chromophore (1998-2000). Under the increased time resolution of the Is fluorescence dynamics measurements, we observed for the first time the low frequency coherent vibrations coupled with the fluorescence decay dynamics (2002), v(1) similar to 140 cm(-1) with damping time tau(1)(d) similar to 500 fs and v(2) - 50 cm(-1) with r(2)(d) similar to 250 fs. When the PNS structure becomes more disordered by mutation, tau(1)(d) is essentially unchanged, but tau(2)(d) becomes shorter. accompanied by a slow-down of the chromophore twisting by mutation, and in the denatured PYP, both coherent oscillations disappear in the completely disordered environment. In view of these results, we have proposed possible mechanisms for the twisting and isomerization of the chromophore in the excited electronic state, where both of the coherent modes vi and v, play crucially important roles in the well-ordered PNS. We have investigated also the supremely important role of the well-ordered PNS in the ultrafast twisting and isomerization of the photoexcited chromophore of the PYP by examining the fs fluorescence dynamics of PYP analogues, where the PNS structure appears to be disturbed by a modified chromophore for which the fine adjustment with the PNS is difficult, leading to a very slow twisting and disappearance of the coherent low frequency oscillations in the fluorescence dynamics. (C) 2004 Japanese Photochemistry Association. Published by Elsevier B.V. All rights reserved.