Evidence for a correlation between the photoinduced electron transfer and dynamic properties of the chromatophore membranes from Rhodospirillum rubrum

The dynamic transition in proteins may have a simple explanation

“…[14][15][16][17][18][19][20] The processes for which these associations have generally been made, such as electron transport or ligand binding, [14][15][16] are those involving relatively fast reactions (and under conditions of relatively low hydration, rather than in solution). This is presumably because of a dependence upon the faster motions, which become too slow to allow normal function.…”

“…Some protein functions have been observed to cease with the loss of equilibrium anharmonic dynamics as the protein is cooled through the dynamic transition. Among these are electron tunnelling in Rhodospirullum rubrum chromatophores, 14 some elements of the photocycle of bacteriorhodopsin in hydrated membranes of Halobacterium salinarum, 15 and ligand binding/release in ribonuclease A crystals. 16 This discontinuity is interpreted as a transition from vibrational, harmonic motion at low temperatures to anharmonic motions as the temperature is raised.…”

“…These include Mö ssbauer spectroscopy of the Fe ion in myoglobin, X-ray scattering measurements of the temperature factor in protein crystals, Rayleigh scattering of Mö ssbauer radiation, and neutron scattering to probe the global dynamics of a relatively limited number of proteins. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Depending on the technique and possibly the protein or the nature of the preparation, the sharpness and temperature of this transition may vary somewhat, but has been generally observed between about 180 and 230 K. It is taken to be an intrinsic property of proteins and, as indicated above, has been associated with the onset of protein function. [14][15][16][17][18][19][20] Recent neutron scattering measurements on a thermophilic glutamate dehydrogenase enzyme in solution, under conditions in which enzyme activity is both possible and measurable, failed to show any relationship between an observed dynamical transition at around 220 K and the onset of activity 13 (Fig.…”

Structure, dynamics and reactions of protein hydration water

“…For example, as in glass-forming liquids, proteins exhibit diffusive motions above the transition and are trapped in harmonic potential wells below. Experiments have shown that in several proteins biological function ceases below the dynamical transition (Parak et al 1980;Rasmussen et al 1992;Ferrand et al 1993). An important physical question concerns the environmental effect on the dynamical transition.…”

The denaturation and degradation of stable enzymes at high temperatures

“…It is implicit in the concept of induced fit [57,58] that an enzyme must flex over a time scale in keeping with its catalytic-centre activity, and that changes between conformational substates allow catalytic activity. Enzyme activity has been demonstrated at temperatures below the glass transition [59], where mobility does not occur [60][61][62][63], but catalytic-centre activities are very low, and the significance of this activity is not yet clear.…”