Structural order of lipids and proteins in membranes: evaluation of fluorescence anisotropy data.

Abstract

[2] in which IIl and IV are the time integrals of III and I-. The steady-state FA can be expressed by the time-resolved FA as s= J dtrtIt/ J dtIt, [3] in which the total fluorescence intensity It = I I I + 2Ij has been introduced. Since of x7 was consonant with the general concepts of membrane fluidity. The derivation of Eq. 4 proceeds from the following concept: The polarized light excites dipole moments of a certain orientation that emit light over their lifetime r. Initially the emitted light is polarized parallel, and rt is large. Due to rotational diffusion the orientation of the emitting dipoles becomes increasingly disordered, and rt decreases. Assuming the environment of the dipoles to be isotropic, their final distribution will also be isotropic, and rt decreases to zero (Fig. 1). The larger X and therefore 0, the longer the initially created anisotropy is preserved and consequently detected in steady-state measurements yielding a large rs.Recent time-resolved FA measurements with pure lipid membranes (2-4), lipid membranes containing cholesterol (5, 6), and cell membranes (7,8), as well as earlier measurements* with excitable membranes (9), have shown rt not to decrease to zero but to reach a finite level r. (Fig. 1)

Microsomal lipid peroxidation causes an increase in the order of the membrane lipid domain

“…A significant increase in r(*~) from 0.09 (control) to 0.I 3 by ~50% was observed by microsomal lipid peroxidation to 60 nmol malondialdehyde/mg protein. These values correspond to the conventional order parameter of S = 0.48 (control) and 0.58 (60 nmol malondialdehyde/mg protein), respectively [24,25].…”

Lipid conformation in model membranes and biological membranes

“…A Davis (1979 microviscosity) refers to membranes in general and is independent of the specific technique employed. This is also illustrated by fluorescence spectroscopy, where it has been realized only recently that the interpretation of fluorescence depolarization measurements exclusively in terms of microviscosity is incorrect, but that the fluorescence anisotropy is equally dependent on the ordering of the fluorescent probe in the membrane (Heyn, 1979;Jahnig, 1979). Thus the correct evaluation of fluorescence anisotropy data leads to an order parameter as well as to correlation times.…”

Temperature-Dependent In-Plane Structure Formation of an X-Shaped Bolapolyphile within Lipid Bilayers

“…This method, usually using added fluorescence probes such as diphenylhexatriene, has been extensively used to study order and dynamics in membranes. [34][35][36][37] In our case the fluorescence anisotropy of B12 itself can be studied without the need for additional probes. The temperature dependent measurements of B12 in DPPC show that the fluorescence anisotropy r does not change during the phase transition of almost pure DPPC at 41 ºC, but decreases only at higher temperature in the temperature range of the additional DSC transitions (see Figure 7C).…”