This work is aimed at establishing a quantitative physical understanding of membrane dynamics using modern techniques of electron spin resonance (ESR) spectroscopy developed in the laboratory of Freed and spin-labels closely resembling natural membrane components. The specific projects include the following. Dynamic ESR imaging will be used to make highly accurate macroscopic measurements of lateral diffusion in biomembranes in conjunction with microscopic rotational diffusion and orientational ordering. The fundamental relationship between the diffusion coefficients and the orientational order parameters will be used to quantify the correlation between membrane structure and fluidity in the context of free volume models. Lipid interactions with polypeptides will be studied using the enhanced resolution provided by the new techniques of two-dimensional Fourier Transform (2D-FT)-ESR and of high frequency ESR. This will provide better characterization of bulk lipids and boundary lipids and will provide a direct means of measuring exchange rates between the two regions. These new techniques will also be used to provide enhanced resolution in studies of two-phase regions formed from mixtures of lipids,from lipids with cholesterol containing diacyl glycerols, and how they are affected by addition of polypeptide. Such studies will be extended to investigate the dynamic structure of specialized plasma membrane vesicles which involve the immunoglobulin B receptors. These new techniques will lead to better characterization of the internal configurational dynamics of lipid chains in membranes. Macroscopic diffusion in membranes will be compared with microscopic relative diffusion measured using the new 2D-FT-ESR techniques to study the dynamics of molecular clustering in mixed model membranes. This research is directly relevant to studies of membrane morphology, and thus could particularly benefit a wide variety of disciplines where it is important to probe the physical response of membranes. Possible clinical applications include the study of transmembrane drug delivery mechanisms, detection of membrane changes during the immune response, and diagnosis of membrane disorders in diseases of the blood, lungs, liver and kidney.
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