| The studies reported in this thesis demonstrate the versatility of cysteine and cysteine-containing peptides for controlling membrane behavior. The first experimental chapter is a study of the effect of cysteine-mediated dimerization on the membrane activity of an oligopeptide. In particular, an oligopeptide with sequence (KL)3C has been synthesized which can be reversibly dimerized via cysteine-cystine oxidation and reduction. Zwitterionic and negatively charged vesicles have been used as model biomembranes to examine the effects of dimerization on the peptide-membrane interactions and to evaluate the dimerization potential for drug delivery carriers. Vesicle leakage (by entrapped calcein release) and aggregation (using quasi-elastic light scattering), as a result of the interactions with the peptide have been studied. The extent of binding of both peptide forms to model membranes has been measured and a theoretical model has been proposed that shows that simple electrostatics may largely account for the peptide behavior. The peptide-mediated cellular uptake of a marker molecule has been explored and the results also suggested the importance of the electrostatic interactions.; The second experimental chapter reports on the stable adhesion of vesicles on a gold surface modified by chemisorption of acetyl-cysteine, for potential application in sensor chips. Because vesicles may entrap thousands of reporter molecules, strong signal amplification can be obtained if a small number of analytes can simply release the entrapped reporters. To achieve this goal, vesicles must first be stably adhered to a surface, without rupture. Vesicle composition and charge (zwitterionic, negative), and solution ionic strength, were varied to study the adhesion of fluorescent vesicles to glass, gold, and gold modified with chemisorbed acetyl-cysteine. Vesicle fusion (by energy transfer) and stable adhesion of intact vesicles (with entrapped calcein) were monitored using confocal fluorescence microscopy. Diffusion coefficients (by photobleaching recovery) were also determined. Acetyl-cysteine modified gold surfaces were shown to be the more appropriate substrates for adhesion of intact vesicles. Finally, as a ‘proof of principle’, release of a self-quenching entrapped reporter dye (calcein) by the detergent Triton X-100 was followed in real time. |
