Research Interests: Kinetics, Multidisciplinary, Lasers, Ph, Bacteria, and 17 moreMembrane transport, Light, Bacteriorhodopsin, Spectrophotometry, Schiff bases, Anions, Hydrogen isotopes, Mathematical Model, Schiff Base, Charge Transport, Hydrogen-Ion Concentration, Protons, Organic Compound, Halobacterium, Elementary Particles, Purple Membrane, and Charged Particles
Photobleaching of bacteriorhodopsin (BR) by continuous light has recently been demonstrated. This bleaching consists of at least two subsequent product states. One of them is absorbing maximally in the blue spectral region. Our present... more
Photobleaching of bacteriorhodopsin (BR) by continuous light has recently been demonstrated. This bleaching consists of at least two subsequent product states. One of them is absorbing maximally in the blue spectral region. Our present study shows that upon illumination of the bleached sample with blue light a back photoprocess appears, resulting in regeneration of the original BR state. From a
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Absorption kinetic measurements at alkaline pH, in which bacteriorhodopsin (BR) is pre-excited by another flash, indicate that a part of the recovery of the BR ground-state is faster than the decay of the N intermediate of the photocycle.... more
Absorption kinetic measurements at alkaline pH, in which bacteriorhodopsin (BR) is pre-excited by another flash, indicate that a part of the recovery of the BR ground-state is faster than the decay of the N intermediate of the photocycle. This fact proves the existence of a parallel pathway in the late part of the BR photocycle (the decay of Ms into BR), which does not include the N intermediate. We demonstrate that the decay of the Mf intermediate does not lead to any direct recovery of the BR ground-state, and that excitation of N does not form an M-like intermediate. Mf decays directly into the N intermediate, and photoexcitation of N leads to the formation of a red-shifted form, O*. The kinetics of this red-shifted intermediate are also presented.
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Kinetic curves for the bacteriorhodopsin (BR) photocycle were obtained both at 570 and at 412 nm at a series of increasing levels of intensity of the exciting laser. Singular value decomposition (SVD) of these curves showed two... more
Kinetic curves for the bacteriorhodopsin (BR) photocycle were obtained both at 570 and at 412 nm at a series of increasing levels of intensity of the exciting laser. Singular value decomposition (SVD) of these curves showed two transitions in the kinetic profiles that occurred at specific levels of actinic light. This means that the photocycle was influenced by photon density in two ways. In a separate application of SVD, time-resolved optical spectra were analyzed at each of many levels of exciting laser intensities. The studies showed that the transition at the low level of laser intensity was due principally to an increase in the amount of BR that was turning over. The transition at the higher level of laser intensity showed a fundamental change in kinetics of the photocycle. At low intensity levels, the fast form of M (Mf) predominated, whereas at high levels the slow form of M (Ms) predominated. A distinction was found between Mf and Ms, in that the former decayed directly to the O intermediate whereas the latter decayed directly to BR.
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The rate constants of thermal (irreversible) damage of bacteriochlorin pigments (bacteriochlorophyll monomer [B], bacteriochlorophyll dimer [P] and bacteriopheophytine [H]) in reaction center [RC] protein from the photosynthetic bacterium... more
The rate constants of thermal (irreversible) damage of bacteriochlorin pigments (bacteriochlorophyll monomer [B], bacteriochlorophyll dimer [P] and bacteriopheophytine [H]) in reaction center [RC] protein from the photosynthetic bacterium Rhodobacter sphaeroides were studied in the dark and during intense (400 mW x cm(-2)) laser light excitation (wavelengths 488 and 515 nm) under deoxygenated conditions. While the kinetics of degradation of P and B were monoexponential, the decay kinetics of H were overlapped by an initial lag phase at elevated (>40 degrees C) temperature. This is explained by removal of the central metal ion from the bacteriochlorophylls as part of their degradation processes. At all temperatures, the rates of damage were very similar for all bacteriochlorin pigments and were larger in the light than in the dark. The logarithm of the rate constant of pigment degradation and loss of photochemistry as a function of reciprocal (absolute) temperature (Arrhenius/Eyri...
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A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50–60°C. The photobleaching also increases... more
A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50–60°C. The photobleaching also increases with increasing pH from 7 to 10. We suggest that the bleaching at its final stage could be due to the dissociation of the retinal and a local thermal denaturation-like
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Azide has previously been shown to have an effect on the photocycle of bacteriorhodopsin mutants. In appropriate mutants, both the proton release from the Schiff base and reprotonation are accelerated. However, no effect on native... more
Azide has previously been shown to have an effect on the photocycle of bacteriorhodopsin mutants. In appropriate mutants, both the proton release from the Schiff base and reprotonation are accelerated. However, no effect on native bacteriorhodopsin has been found. In this work, we show that protonated azide influences the photocycle of native bacteriorhodopsin, although to a lesser extent than in
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ABSTRACT The transient absorption of bacteriorhodopsin (BR) in native purple membranes (pms) and in pms subjected to proteolytic digestion by trypsin and papain was studied at 297 and 275 nm. The decay kinetics at these wavelengths were... more
ABSTRACT The transient absorption of bacteriorhodopsin (BR) in native purple membranes (pms) and in pms subjected to proteolytic digestion by trypsin and papain was studied at 297 and 275 nm. The decay kinetics at these wavelengths were compared with the kinetics of decay of the M intermediate at 412 nm and the regeneration of BR at 570 nm. The measured flash-induced absorption changes have different kinetics. At 570 nm the absorption change decays more slowly than at 412 nm, and the decays at 297 and 275 nm (after excitation) are even slower. This relationship between the lifetimes is maintained after proteolytic digestion of BR. Multiexponential deconvolution of the decay curves reveals up to three components with different lifetimes and different amplitudes at each wavelength. In particular, the observed slow decay in the UV region is due to the large amplitude of the long-lived components present at 570 and 412 nm, and the lack of the fast component. Therefore no UV signal due to changes in the protein is found to occur independently of the retinal transition.