Quantitative method for studying orientation of transition dipoles in membrane vesicles of spherical symmetry

Pigmented vesicular membranes embedded in polyacrylamide gel exhibit linear dichroism when the gel sample is squeezed [Abdourakhmanov, I.A., Ganago, A.O., Erokhin, Yu.E., Solov'ev, A.A. and Chugunov, V.A. (1979) Biochim. Biophys. Acta 546, 183-186]. The orientation technique of gel-squeezing was modified to enhance polarization effects in membrane vesicles of spherical symmetry. Model calculations were carried out to provide a tool for the quantitative evaluation of the dichroism of squeezed gel samples. The orientation angles of the dipoles can be calculated with reasonable precision by measuring two quantities: (i) the macroscopic deformation parameter of the gel sample, and (ii) a parameter (e.g. the polarization ratio of the fluorescence emission) characterizing the orientation of the transition dipoles in the membranes embedded in the squeezed gel. The validity of the model was confirmed through a series of polarization measurements relating to the fluorescence of chlorophyll a in membranes of osmotically shocked chloroplasts, 'blebs'.