Ultraschallspektrometrie zum dynamischen Verhalten von Domänen in peptidhaltigen Lipidmembranen

Abstract

In this thesis the influence of peptides on lipid membranes in vicinity of the main phase transition is investigated using ultrasonic spectrometry. For these experiments unilamellar vesicles made of 1,2-dimyristoyl-sn-3-glycero-phosphocholine (DMPC) are used. The peptide alamethicin is added in various concentrations.The phase transition is accompanied by domain formation processes and fluctuations of thermodynamic parameters like fluctuations of the density. An increase of fluctuations is observed near the transition temperature, which can be described by an power law for so-called critical systems.Ultrasonic spectrometry probes to changes of the lipid volume during the phase transition. The results show that the spectra have to interpreted by a critical contribution and additional single-time relaxation processes. The latter correspond to the axial diffusion of lipids and rotational isomerization of the alkyl chains. In the vicinity of the phase transition one has to regard another single-time relaxation, which can be interpreted as local deformations of the vesicle.The insertion of alamethicin can be explained by the "membrane thinning" theory in three different concentration depending stages, which can be determined by sound velocimetry. Over the whole concentration range one can observe, that the fluctuations are slowed down by alamethicin.Using ultrasonic spectrometry one can find, that the axial diffusion shows a strong coupling to the critical behavior in presence of alamethicin.The amplitude of the spectral term of the vesicle deformation increases by addition of alamethicin and may be coupled to the lysis of the membrane induced by alamethicin. The vesicle deformation shows also strong coupling to the critical behavior.