[77] Laser light scattering techniques for determining size and surface charges of membrane vesicles from cyanobacteria

This chapter illustrates the application of quasi-elastic laser light scattering (QELS) and laser Doppler velocimetry (LDV) to the determination of volumes and surface charges of plasma (CM) and thylakoid (intracellular, ICM) membrane vesicles prepared from normal and salt-stressed cyanobacteria according to a recently established method. Laser light scattering techniques allow accurate determination not only of the diffusion coefficient and, hence, the volume of membrane vesicles but also of intact cells. The surface potential is also obtained by these techniques which have the great advantage of being noninvasive. When a beam of monochromatic light is scattered by a suspension of identical particles the scattered light spectrum has a Lorentzian shape. This is because of the Doppler frequency shift provoked by the random motion of the particles in suspension. Electrophoretic mobility measurements lead to the determination of the electrokinetic potential which reflects the surface charge at the shear plane of the particle. It is emphasized that of all different methods, QELS is the only one that provides immediate results without any modification of the biological sample.