Ligand-Receptor Contact Interactions Using Self-Assembled Bilayer Lipid Membranes
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Mat. Res. Soc. Symp. Proc. Vol. 360 01995 Materials Research Society
decane. Into these s-BLMs, three classes of compounds have been embedded as follows: (a) Electron acceptors, donors, and mediators including highly conjugated compounds such as mesotetraphenylporphyrins (TPP), metallo-phthalocyanines (PLC), TCNQ (tetracyano-p-quinodimethane), TTF (tetrathiafulvalene), BEDT-TTF (bis-ethyldithio-tetrathiafulvalene), and tetraseleno-fulvalene), (b) Redox proteins and metalloproteins such as cytochrome c, and ironsulfur proteins (ferrodoxins and thioredoxins). Also included in this class are compounds partaking in ligand-receptor contact interactions; specifically, the ligand may be a substrate, an antigen, a hormone, ions, or an electron acceptor or a donor, and the corresponding receptor embedded in s-BLM may be an enzyme, an antibody, a protein complex, a carrier, a channel, or a redox species [1,3,4], and (c) Fine semiconductor particles (formed in situ) such as CdS, CdSe, and AgCI [7]. We have worked with some of these compounds in the past in conjunction with conventional BLMs. Hence, methodologies developed for in situ formation of semiconductor particles on conventional BLMs can be applied to s-BLM systems. Mention should be made that in s-BLMs, albeit attractive for certain purposes as described in this paper, the metallic substrate precludes ion translocation across the lipid bilayer. Therefore, the pursuit of a simple method for obtaining long-lived, planar BLMs separating two aqueous media has been an elusive one until now (H. Yuan, S. Hua and H. T. Tien, results of 1991-93, to be published). A brief description of forming a planar BLM on agar gel will be given below. Techniques for agar gel supported BLMs. The formation procedure consists of three steps. In the first step, a chlorided Ag wire (Ag/AgCl) is inserted into a Teflon tubing which has been previously filled with a mixture of agar and KCI solution saturated with AgCl. The AgC1 electrode and the filled Teflon tubing are glued together with wax at the point of insertion. In this way an Ag/AgC1-Teflon tubing salt bridge (sb) is constructed. In the second step, the tip of the other end of the Teflon salt bridge is cut in situ while immersed in a BLM-forming solution with a sharp knife, as done with the s-BLM technique. In the third and last step, the Ag/AgC1-Teflon salt bridge with the tip freshly coated with lipid solution is then immersed in 0.1 M KC1 solution in the cell chamber. Alternatively, the second step described above may be carried out in air and then the freshly cut end of the salt bridge is immediately immersed in the lipid solution for a few minutes. In either case, the cell chamber filled with an appropriate aqueous solution (e.g., 0.1 M KCI) contains a Ag/AgC1 reference electrode and a Ag/AgCI-Teflon salt bridge with a self-assembled BLM at its end. The lead wires of the two electrodes are connected to the measuring instrumentation [26]. In this connection, it should be noted that the salt bridge (sb) shown in Fig. 1 may be identif
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