Plane membrane

Taylor et al. [156] suggested that the crystals belong to the two-sided plane group C12, in which there are four ATPase molecules per unit cell of 9 113 A, with ATPase dimers related by a two-fold rotational axis within the membrane plane parallel to the b cell axis. While the arrangement of ATPase molecules was highly ordered within... 

Similar instability is caused by the electrostatic attraction due to the applied voltage [56]. Subsequently the hydrodynamic approach was extended to viscoelastic films apparently designed to imitate membranes (see Refs. 58-60, and references therein). A number of studies [58, 61-64] concluded that the SQM could be unstable in such models at small voltages with low associated thinning, consistent with the experimental results. However, as has been shown [60, 65-67], the viscoelastic models leading to instability of the SQM did not account for the elastic force normal to the membrane plane which opposes thickness... 

The second issue concerns the anisotropy of the membrane. The models presented in this section all assume that the membrane has the symmetry of a chiral smectic-C liquid crystal, so that the only anisotropy in the membrane plane comes from the direction of the molecular tilt. With this assumption, the membrane has a twofold rotational symmetry about an axis in the membrane plane, perpendicular to the tilt direction. It is possible that a membrane... 

It is also possible that a membrane might have an even lower symmetry than a chiral smectic-C liquid crystal in particular, it might lose the twofold rotational symmetry. This would occur if the molecular tilt defines one orientation in the membrane plane and the direction of one-dimensional chains defines another orientation. In that case, the free energy would take a form similar to Eq. (5) but with additional elastic constants favoring curvature. The argument for tubule formation presented above would still apply, but it would become more mathematically complex because of the extra elastic constants. As an approximation, we can suppose that there is one principal direction of elastic anisotropy, with some slight perturbations about the ideal twofold symmetry. In that approximation, we can use the results presented above, with 4) representing the orientation of the principal elastic anisotropy. 

Fig. 1. The structure of the LHCII monomer as derived from electron crystallography [51], A proposed topography of the polypeptide in the photosynthetic membrane. Letters A, B and C indicate the three hydrophobic ix-helices spanning the membrane. Chlorophyll molecules are arranged into two rings roughly parallel to the membrane plane. B Approximate position of the chlorophyll in the upper level (left) and lower level (right) on the membrane plane. Dashed lines outline a-helices A, B and C. Chlorophyll molecules are oriented perpendicular to the membrane plane and are thus represented as black bars. Chlorophylls numbered as 6,7 and 8 are closer to those belonging to the lower layer than the other pigment molecules...

Fig. 2. Models for the organisation of PSII in the membrane plane. Model in (A) is from Peter and Thomber [9]. Model in (B) is from Harrison e Melis [100]. b2c and b3 indicates two kinds of LHCII trimers with and without the Lhchi gene product. Model in (C) is from Dainese et al. (1992) [251] LHCII a, b and c indicates respectively the unphosphorylateable-non mobile, the phosphorylateable-non mobile and the phosphorylatable-mobile pools of LHCII. Model in (D) is from Jansson (1993) [252]. For the sake of simplicity the same nomenclature has been used, where possible, to indicate the complexes...

The chemical reaction does have a vector character along the axis normal to the membrane plane in which the transport takes place. There is the reducing half reaction on one side of the membrane and the oxidizing half on the other side. 

The 88 antenna Chls are roughly segregated to the upper and lower membrane planes (Fig. 1, third row), but aside from this little spatial order is evident. What is particularly striking in the space filling views is that, aside from the region immediately surrounding the RC, the Chls fill almost the entire volume of the protein. 

Fig. 1. Space filling in Photosystem I illustrated from three points of view above file membrane plane (top), side view (bottom) and in between (middle). The left hand column shows the Chls in PSI with the special pair highlighted in black. The middle column contains all of the atoms in the structure with the Chls in black. The right hand column depicts the Chls in the licorice representation.

Figure 23-34 Structure of PSII with assignment of protein subunits and cofactors. (A) Arrangement of transmembrane a-helices and cofactors in PSII. One monomer of the dimer is shown completely, with part of the second monomer related by the local-C2 axis (filled ellipse on the dotted interface). Chlorophyll a head groups and hemes are indicated by black wire drawings. The view direction is from the luminal side, perpendicular to the membrane plane. The a-helices of Dl, D2, and Cyt b-559 are labeled. D1/D2 are highlighted by an ellipse and antennae, and CP43 and CP47 by circles. Seven unassigned a-helices are shown in gray.

A few transmembrane molecular rods having different lengths and terminal shapes and moving freely by lateral diffusion may bind to a given receptor-transmitter on one side (left) of the membrane in a configuration in the membrane plane and in a displacement perpendicular to the membrane that will depend on the disposition and depth of the binding sites on the transmitter. This will impose on the... 

Structural information about cytochrome oxidase is very limited beyond the level of primary structure as it has proved impossible to grow crystals of sufficiently high quality for high resolution X-ray studies. Cytochrome oxidase is a transmembrane protein which is inserted asymmetrically through the membrane. The overall shape is like a Y, with the stalk extending about 50 A above the membrane plane on the... 

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