Bilayer photoreceptor

It should be pointed out that a specific modification of Ti(0)Pc 1 (R = -H) in organic polymers is the most widely used photoconductor in bilayer photoreceptor copiers and laser printers [19]. A thin film containing ethylene-bridged silicon phthalocyanine polymer dispersed in poly(vinylidene fluoride) (1 4 by weight) obtained by casting from a DMF slurry on quartz was orientated in an electrical field [20], A double-layered receptor device for measuring the... 

Figure 10.3. Schematics of the configuration and the photodischarge process of a bilayer photoreceptor (CGL charge generation layer CTL charge transporting layer).

Figure 10.9. Spectral response curve of an InClPc bilayer photoreceptor device. (Reproduced from ref 114, Copyright 1987, The Society for Imaging Science and Technology.)...

Figure 10.30. (a) Action spectra of perylene XXa in a bilayer photoreceptor device, (upper curve) illumination through the CTL, (lower curve) illumination through the semi-transparent aluminium substrate (b) absorption spectrum of an evaporated film of XXa ( 1700 A) (Reproduced from ref 247, Copyright 1988, North-Holland). 

Table 10.12. Xerographic data of Sq-1 and Sq-25 in bilayer photoreceptor devices ...

M FIGURE 5-13 Structural model of bacteriorhodopsin, a multipass transmembrane protein that functions as a photoreceptor in certain bacteria. The seven hydrophobic a helices in bacteriorhodopsin traverse the lipid bilayer. A retinal molecule (red) covalently attached to one helix absorbs light. The large class of G protein-coupled receptors in eukaryotic cells also has seven membrane-spanning a helices their three-dimensional structure is similar to that of bacteriorhodopsin. [After H. Luecke et al., 1999, J. Mol. Biol. 291 899.]... 

Stryer L 1986 Cyclic GMP cascade of vision Anna. Rev. Neurosci. 9 87-119 Cafiso D S and Hubbell W L 1980 Light-induced interfacial potentials in photoreceptor membrane Biophys. J. 30 243-63 Drain C M, Christensen B and Mauzerall D 1989 Photogating of ionic currents across a lipid bilayer Proc. Natl Acad. Sci. USA 86 6959-62 Vsevolodov N N, Druzhko A B and Djukova T V 1989 Actual possibilities of bacteriorhodopsin application Molecular Electronics Biosensors and Biocomputers ed F T Hong (New York Plenum) pp 381-4 Vsevolodov N N and Dyukova T V 1994 Retinal-protein complexes as optoelectronic components Trend. Biotechnol. 12 81-103 Vsevolodov N N, Djukova T V and Druzhko A B 1989 Some methods for irreversible write-once recording in Biochrom films Proc. Annu. Int. Conf IEEE Eng. Med. Biol. Soc. 11 1327... 

Other proteins that have activities that correlate with the mesomorphic tendencies of the lipid bilayer include the vertebrate photoreceptor protein rhodopsin (42) and a dolichylphosphomannose synthase (43). The paucity of other examples reflects the lack of systematic studies. Membrane protein reconstitutions are generally difficult to perform, especially if the lipid composition is to be varied, and, therefore, are unlikely to be undertaken without good reason. Studies of correlations with lipid mesomorphic tendencies, stimulated by research such as that reported here, are now under consideration by several biochemical groups. Certainly, much more work is needed in this area. 

The vertebrate rod photoreceptor cell (Fig. 1) contains in its outer segment some 1000-2000 regularly stacked flat sacs. The membrane of these sacs, the photoreceptor membrane, consists - like all biomembranes - of a lipid bilayer and membrane protein. Its major... 

Reconstitution of the delipidated photoreceptor membrane or rhodopsin preparations with selected phospholipids is achieved by shaking them together with additional DTAB for 1 h (Hong Hubbell, 1973). The detergent is then removed by the dialysis procedure described in the previous paragraph. Recovery of rhodopsin ranges from 80-100%. Freeze-fracture electronmicroscopy shows that rhodopsin is incorporated into lipid bilayer structures (Chen Hubbell, 1973). 

Phospholipase-C treatment of the photoreceptor membrane also has a proununced affect on the extent to which rhodopsin is attacked by proteolytic enzymes (van Breugel et al., 1975). In the case of untreated membranes rhodopsin is partially degraded by incubation with pronase without a marked loss of 500 nm absorbance (Fig. 7, bottom right). After prior treatment of the membranes with phospholipase-C there is a subtantial loss of 500 nm absorbance (Fig. 7, top left), and gel electrophoresis shows that this is accompanied by more extensive digestion of the rhodopsin molecule. Control experiments indicate that this is not due to the effect of phospholipase per se (Fig. 7, bottom left) and that the effect does not occur when phos-pholipase-C treatment follows that with pronase (Fig. 7, top right). These findings indicate that removal of phospholipids makes the rhodopsin molecule more vulnerable to attack by proteolytic enzymes. Thus rhodopsin must normally be deeply embedded in the hydrophobic core of the phospholipid bilayer with only a small part of the molecule exposed to the aqueous phase. 

The chemistry of ROS has been studied by several laboratories, and recently reviewed by Daemen (1973). Over 90% of the protein is rhodopsin, a photosensitive glycoprotein of molecular weight around 35,000, which is imbedded in a lipid bilayer. Phospholipids make up about 96% of the lipids of cattle ROS and cholesterol is the major component of the neutral lipid fraction. Phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) are the major phospholipids in all species examined, with phosphatidyl serine (PS), phosphatidyl inositol (PI), and sphingomyelin (SPh) present in lesser amounts (Anderson and Maude, 1972). Detailed analysis of the photoreceptor membranes of vertebrate species ranging from frogs to humans have revealed a fairly constant phospholipid class and protein composition (Basinger and Anderson, unpublished). 

Single-layer photoreceptor devices have always been very attractive for economic reasons. The continuous improvement in the bilayer device technology, in terms of photoelectrical and mechanical properties, has made re-introduction of the single-layer concept difficult. However, single-layer devices may re-surface at the low end with today s improved materials and know-how. At the low end, providing the performance is adequate, cost is a big driver. 

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