Pigmented bilayer lipid

Pigmented Bilayer Lipid Membranes, Chlorophyll molecules have been incorporated into two types of artificial bllayer lipid membrane systems for the study of photoenergy transduction. The first consists of a planar bllayer lipid membrane (BLM) separating two aqueous solutions where photovoltaic effects can be Induced. The second system comprises liposomes which are Ideally suited for studies of photo-induced permeability, spectroscopy and chemical reactions. For more complete technical details, two pertinent publications are available (42,43). 

Hong F T 1976 Charge transfer across pigmented bilayer lipid membrane and its... 

The use of pigmented bilayer lipid membranes (p-BLMs) has yielded a wealth of... 

Pigmented Bilayer Lipid Membranes as a Model for the Thylakoid Membrane... 

Table /. Orientation of carotenoid pigments in lipid bilayers...

The chain of redox processes taking place under illumination at the interfaces between a bilayer lipid membrane and electrolyte causes a photopotential to be set up.92 95 The stationary values of the photopotential depend on the redox potentials of the components in aqueous solutions. The spectral dependence of the photopotential corresponds approximately to the absorption spectrum of the pigment, while the photopotential depends on the... 

The photosynthetic pigment chlorophyll mediates the primary act of photosynthesis in higher plants. However, chlorophyll can also catalyze electron transfer reactions at oil/water interfaces and on bilayer lipid membranes without illumination [2, 7, 38]. The reversible chemical reduction of chlorophyll by zinc was first studied by Timiriazeff [44], and the role of chlorophyll in oxidation-reduction reactions has been the subject of numerous later investigations [45],... 

It is known that chlorophyll molecules are orientated at an average angle of 30-35 away from the hi layer in thylakoid membranes (4,5) and it has recently been proposed that this is due to a similar orientation of the transmembrane a-helical domains of the pigment-proteins (1,6). It is proposed that one tetrapyrrole ring fits on each side of the bilayer, aligned parallel to the principal axis of the protein and therefore at 30-35° to the bilayer normal - see Fig. 5, ref 1. Thermodyneimic considerations would then favour the alignment of the phytyl chains of the chlorophylls parallel to the bilayer normal at the protein-acyl lipid interface where they would be free to interact with the acyl chains of the bilayer lipids (6). 

On the basis of X-ray diffraction studies, the ultrastructure of chloroplast membrane has been analyzed by Kreutz - s, and the subject reviewed by him. Using the freeze-etching technique, Muehlethaler has suggested a picture for the thylakoid membrane based upon the bimolecular leaflet model. The salient feature in all these proposed models lies in their oriented bilayer lipid core, onto which other important cellular constituents, such as proteins and pigments, may interact through either ionic or van der Waals attraction, or both. Muehlethaler s interpretation is of special interest, in view of the experiments using the pigmented... 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Sujak, A., K. Strzalka, and W.I. Gruszecki. 2007b. Thermotropic phase behaviour of lipid bilayers containing carotenoid pigment canthaxanthin A differential scanning calorimetry study. Chem. Phys. Lipids 145 1-12. 

As discussed above, the photosynthetic reaction center solves the problem of rapid charge recombination by spatially separating the electron and hole across the lipid bilayer. In order to achieve photoinitiated electron transfer across this large distance, the reaction center uses a multistep sequence of electron transfers through an ensemble of donor and acceptor moieties. The same strategy may be successfully employed in photosynthesis models, and has been since 1983 [42-45]. The basic idea may be illustrated by reference to a triad Dj-D2-A, where D2 represents a pigment whose excited state will act as an electron donor, Di is a secondary donor, and A is an electron acceptor. Excitation of D2 will lead to the following potential electron transfer events. 

The primary photosynthetic process is carried out by a pigment protein complex the reaction centre (RC) embedded in a lipid bilayer membrane (Figure 6.19) and surrounded by light-harvesting complexes.1477,1481,1482 Thus energy is transferred from LH1 to a bacteriochlorophyll special pair (P) and then through a bacteriochlorophyll molecule (BC monomer) to bacteriopheophytin (BP a chlorophyll molecule lacking the central Mg2 + ion), followed by electron transfer to a quinone Qa in hundreds of ps. The neutral P is then restored by electron transfer from the nearest intermembrane space protein cytochrome c (Cyt c) in hundreds of ns. The rate constants of the... 

---