Orientation and mobility of molecules in membranes studied by polarized light spectroscopy

Abstract

Biological membranes are composed of mainly lipids and proteins. The physical properties of the lipids, forming a bilayer structure, are of crucial importance for the living cell, since the plasma membrane is the guardian barrier towards the environment. Thus, the functioning cell needs a highly stable lipid bilayer, which depends on molecular packing and orientation properties of the various membrane components (Wieslander et al. 1980). The spatial arrangement of the membrane proteins incorporated in the lipid matrix plays an essential role for the different chemical processes occurring at or within the membrane. Information about molecular orientation and mobility is therefore necessary for unravelling the functional mechanisms of a biological membrane.

Anisotropic circular dichroism signatures of oriented thylakoid membranes and lamellar aggregates of LHCII

“…The presence of the strong pigmentpigment interactions in these systems makes the use of non-invasive, polarization spectroscopy techniques, such as linear dichroism (LD) and circular dichroism (CD), a valuable tool in elucidating their molecular architecture. The theoretical background, technical approaches and applicability of these methods in photosynthesis research have been covered in a number of books and review articles (Bloemendal and van Grondelle 1993;Clayton 1980;Garab 1996;Garab and van Amerongen 2009;Hofrichter and Eaton 1976;Johansson and Lindblom 1980;Norden et al 1992;Pearlstein 1991;van Amerongen and Struve 1995;van Amerongen et al 2000). As chirality can occur at different levels of structural complexity of the pigment system, CD spectroscopy can provide information on different levels of hierarchically organized assemblies (Garab and van Amerongen 2009).…”

SPECTROSCOPIC AND ORIENTATIONAL PROPERTIES OF CHLOROPHYLL a AND CHLOROPHYLL b IN LIPID MEMBRANES

“…The order parameter S, can now he written in terms of order parameters, describing the average orientation of the molecular frame in the sample frame (a,,,,), and angles of the transition moments in the molecular frame (a,,,*) by making use of the closure relation of the Wigner rotation matrix elements (Johansson and Lindblom, 1980;Zannoni, 1979;van Gurp ct al., 1988a):…”

Lipid phase structure governs the regulation of lipid composition in membranes of acholeplasma laidlawii

“…Physicochemical properties of cholesterol in model membranes have been extensively studied. In [24,25] the lipid lateral diffusion in a bilayer was almost unaffected by incorporation of cholesterol. However, the order par~eter of the hydrocarbon chains, which reflects the average chain conformation, was markedly increased [24].…”