411 research outputs found
Structures of the intermediates in the catalytic cycle of mitochondrial cytochrome c oxidase
Cytochrome c oxidase is the terminal complex of the respiratory chains in the mitochondria of nearly all eu-karyotes. It catalyzes the reduction of molecular O-2 to water using electrons from the respiratory chain, delivered via cytochrome c on the external surface of the inner mitochondrial membrane. The protons required for water formation are taken from the matrix side of the membrane, making catalysis vectorial. This vectorial feature is further enhanced by the fact that the redox catalysis is coupled to the translocation of protons from the inside to the outside of the inner mitochondrial membrane. We are dealing with a molecular machine that converts redox free energy into a protonmotive force (pmf). Here, we review the current extensive knowledge of the structural changes in the active heme-copper site that accompany catalysis, based on a large variety of time-resolved spectroscopic experiments, X-ray and cryoEM structures, and advanced computational chemistry.Peer reviewe
Fluctuation-Induced Interactions between Rods on Membranes and Interfaces
We consider the interaction between two rods embedded in a fluctuating
surface which is governed by either surface tension or rigidity. The
modification of fluctuations by the rods leads to an attractive long-range
interaction that falls off as with their separation. The orientational
dependence of the resulting interaction is non-trivial and may lead to
interesting patterns of rod-like objects on such surfaces.Comment: Revtex, 10 pages, one figur
Collective shuttling of attracting particles in asymmetric narrow channels
The rectification of a single file of attracting particles subjected to a low
frequency ac drive is proposed as a working mechanism for particle shuttling in
an asymmetric narrow channel. Increasing the particle attraction results in the
file condensing, as signalled by the dramatic enhancement of the net particle
current. Magnitude and direction of the current become extremely sensitive to
the actual size of the condensate, which can then be made to shuttle between
two docking stations, transporting particles in one direction, with an
efficiency much larger than conventional diffusive models predict
Diffusion-controlled generation of a proton-motive force across a biomembrane
Respiration in bacteria involves a sequence of energetically-coupled electron
and proton transfers creating an electrochemical gradient of protons (a
proton-motive force) across the inner bacterial membrane. With a simple kinetic
model we analyze a redox loop mechanism of proton-motive force generation
mediated by a molecular shuttle diffusing inside the membrane. This model,
which includes six electron-binding and two proton-binding sites, reflects the
main features of nitrate respiration in E. coli bacteria. We describe the time
evolution of the proton translocation process. We find that the electron-proton
electrostatic coupling on the shuttle plays a significant role in the process
of energy conversion between electron and proton components. We determine the
conditions where the redox loop mechanism is able to translocate protons
against the transmembrane voltage gradient above 200 mV with a thermodynamic
efficiency of about 37%, in the physiologically important range of temperatures
from 250 to 350 K.Comment: 26 pages, 4 figures. A similar model is used in arXiv:0806.3233 for a
different biological system. Minor changes in the Acknowledgements sectio
Phase Behaviour of Amphiphilic Monolayers: Theory and Simulation
Coarse grained models of monolayers of amphiphiles (Langmuir monolayers) have
been studied theoretically and by computer simulations. We discuss some of the
insights obtained with this approach, and present new simulation results which
show that idealised models can successfully reproduce essential aspects of the
generic phase behaviour of Langmuir monolayers.Comment: To appear in J. Phys.: Cond. Matte
Structure of symmetric and asymmetric "ripple" phases in lipid bilayers
We reproduce the symmetric and asymmetric ``rippled'' states of
lipid membranes by Monte Carlo simulations of a coarse-grained molecular model
for lipid-solvent mixtures. The structure and properties compare favorably with
experiments. The asymmetric ripple state is characterized by a periodic array
of fully interdigitated ``defect'' lines. The symmetric ripple state maintains
a bilayer structure, but is otherwise structurally similar. The formation of
both ripple states is driven by the propensity of lipid molecules with large
head groups to exhibit splay.Comment: 4 pages, 4 figure
Proton Wires in an Electric Field: the Impact of Grotthuss Mechanism on Charge Translocation
We present the results of the modeling of proton translocation in finite
H-bonded chains in the framework of two-stage proton transport model. We
explore the influence of reorientation motion of protons, as well as the effect
of electric field and proton correlations on system dynamics. An increase of
the reorientation energy results in the transition of proton charge from the
surrounding to the inner water molecules in the chain. Proton migration along
the chain in an external electric field has a step-like character, proceeding
with the occurrence of electric field threshold-type effects and drastic
redistribution of proton charge. Electric field applied to correlated chains
induces first a formation of ordered dipole structures for lower field
strength, and than, with a further field strength increase, a stabilization of
states with Bjerrum D-defects. We analyze the main factors responsible for the
formation/annihilation of Bjerrum defects showing the strong influence of the
complex interplay between reorientation energy, electric field and temperature
in the dynamics of proton wire.Comment: 28 pages, 9 figure
Charge-Reversal Instability in Mixed Bilayer Vesicles
Bilayer vesicles form readily from mixtures of charged and neutral
surfactants. When such a mixed vesicle binds an oppositely-charged object, its
membrane partially demixes: the adhesion zone recruits more charged surfactants
from the rest of the membrane. Given an unlimited supply of adhering objects
one might expect the vesicle to remain attractive until it was completely
covered. Contrary to this expectation, we show that a vesicle can instead
exhibit {\it adhesion saturation,} partitioning spontaneously into an
attractive zone with definite area fraction, and a repulsive zone. The latter
zone rejects additional incoming objects because counterions on the interior of
the vesicle migrate there, effectively reversing the membrane's charge. The
effect is strongest at high surface charge densities, low ionic strength, and
with thin, impermeable membranes. Adhesion saturation in such a situation has
recently been observed experimentally [H. Aranda-Espinoza {\it et al.}, {\sl
Science} {\bf285} 394--397 (1999)]
Fluctuation-Induced Interactions between Rods on a Membrane
We consider the interaction between two rods embedded in a fluctuating
surface. The modification of fluctuations by the rods leads to an attractive
long-range interaction between them. We consider fluctuations governed by
either surface tension (films) or bending rigidity (membranes). In both cases
the interaction falls off with the separation of the rods as . The
orientational part of the interaction is proportional to in the former case, and to in the latter, where and
are angles between the rods and the line joining them. These
interactions are somewhat reminiscent of dipolar forces and will tend to align
collections of such rods into chains.Comment: REVTEX, 14 pages, with 2 Postscript figure
Cytochrome bo from Escherichia coli: identification of haem ligands and reaction of the reduced enzyme with carbon monoxide
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