Our
Group's Studies on bR
You can reach below some research subjects and their abstract.
Modelling
and kinetics of light induced proton pumping of bR
reconstituted liposomes
Photoresponse
of bR immobilized in polyacrilamide
gel membranes.
Kinetic
analysis of light induced prton dissociation and association
of bacteriorhodopsin in purple membrane fragments under
continuous illumination.
Modelling
of long-term photoresponse of bacteriorhodopsin immobilized on
cellulose acetate membranes.
Modelling
and kinetics of light induced proton pumping of bR reconstituted
liposomes 1991
(TOP)
Purple
membrane fragments isolated from the cell membrane of photosynthetic
bacteria Halobacterium halobium S9 strain are incorporated into egg
yolk phosphotidylcholine liposomes. Purple membrane contains
crystalline patches of a retinal protein called bacteriorhodopsin.
Upon illumination, bacteriorhodopsin undergoes a reversible
photoreaction in which a proton is released on one side of the
membrane and a proton is bound on the other side, thus resulting in
an electrochemical gradient across the membrane. The net rate of
proton pumping is the combination of the rates of photoreaction and
of simple diffusion of protons across the lipid membrane to
componsate for the concentration difference between the two sides of
the membrane. A mechanistic model
is also proposed for the photoreaction which includes activation,
proton dissociation, translocation
and association reactions.
Activation and translocation of bacteriorhodopsin are
considered to be fast, but proton dissociation and association steps
are considered to be slow. The resultant rate expression is compared
with light on and light off experimental
data. The model is in accordance with experimental data for initial
pH values around 7.
Photoresponse
of bR immobilizzed in polyacrilamide
gel membranes 1994
(TOP)
A
two-chambered cell has been designed and constructed for the
measurement of photoresponses
of bacteriorhodopsin immobilized
in polyacrylamide
gel (PAG)
membranes. The photoresponse of bacter-iorhodopsin
was determined by measuring the pH variation in each chamber
independently, for long periods of illumination. The aim was to
verify the light driven proton transfer of bacteriorhodopsin
immobilized in PAG membranes. However, the same pH variation was
observed in the two chambers irrespective
of whether oriented or non-oriented bacteriorhodopsin immobilized in
PAG membranes
were employed.
It
has been concluded that upon illumination of the biosynthetic
membrane, protons were not trans-fered from one chamber into
another. The pH variation was then attributed to the association and
dissociation of protons from
bacteriorhodopsin in the membrane. The protonation and deprotonation
of PAG interfered with the photoresponse of bacteriorhodopsin
due to pH disturbance, even though light had
no direct effect on PAG. This might be the main reason for the very
low efficiencies obtained in such energy
transducing biosynthetic membranes.
Kinetic
analysis of light induced prton dissociation and association of
bacteriorhodopsin in purple membrane fragments under continous
illumination. 1995
(TOP)
In
the present work the photo responses of bacteriorhodopsin in purple
membrane fragments were studied under continous high intensity light
illumination in different ranges of pH, temprature and ionic
strength. The activity of bacteriorhodopsin was measured as pH vs.
Time by using combined pH electrode. The activity of
bacteriorhodopsin in purple membrane fragments
at acidic pH was found to be more sensitive to temperature
changes than it was at physiological or higher pH values. The
activity of bacteriorhodopsin was also found to be the function of
varing concentrations of different salts. The kinetic
analyses of light reactions (proton dissociation) and dark reactions
(proton association) were carried out at different pH, temperature
and ionic strengths. The kinetic data revealed that the proton
dissociation in the light and proton association in the dark
followed the first order kinetics in the pH range of 6.7-7.2 at room
temperature. Beyond these limits the kinetic behavior of
bacteriorhodopsin was found to be much more complex.
Modelling
of long-term photoresponse of bacteriorhodopsin immobilized on
cellulose acetate membranes 1996
(TOP)
Purple
membrane fragments with its integrated protein bacteriorhodopsin
were immobilized on lipid impregnated and lipid free cellulose
acetate membranes. Two mathematical models were suggested to
simulate the photoresponse curves of these membranes which were
obtained by measuring the pH variation independently in each chamber
of specifically designed photoactivity cellfor long periods of
illumination. The first order model suggested was mainly based on
the existence of light phase deprotonation and dark phase
reprotonation reactions. The overall deprotonation rate constants
were found to be slightly less than the overall reprotonation rate
constants with the first order kinetics. In the second model, the pH
change-time data were expressed by a mathematical decay function.
There has been found a great agreement between the first order rate
constants and the decay constants.
