The phenomenon of electro-optic orientation was discovered by John Kerr in 1875 and has been used extensively for determining the optical polarizability anisotropy of small molecules and for high-speed transmission of optical signals. Measurements on biopolymers have been made at least since 1950, but only in the last decade have these yielded definitive structural and physical information. In the course of this review, it should become obvious that among the reasons for this late development is the inherent difficulty of analysing optical data that depend simultaneously on intrinsic optical-structural properties of the molecules, and on their degree of orientation under the conditions of the experiment. The problem has been particularly difficult far biopolymers such as the nucleic acids, whose polarization in an electric field is dependent on their special polyelectrolyte properties. These unique electrostatic properties are an important feature in the interpretation of the experimental observations.

This paper consists of three parts. The first describes theoretically a general strategy for fragmentation and separation of membranes which can be used in the elucidation of their structure and function. The second part describes a practical separation method, partition in liquid aqueous polymer two-phase systems, which can be used for separation of macromolecules and membrane particles of biological origin. The third part gives examples of the application of this method to membrane vesicles, and how this separation in combination with the strategy described in the first part can be used for analysis of the structure of biological membranes.

Excitation and conduction in the majority of excitable cells, as originally described in the squid axon, are initiated by a transient and highly selective increase of the membrane Na conductance, which allows this ion to move passively down its electrochemical gradient (Hodgkin & Katz, 1949; Hodgkin & Huxley, 1952). The term ‘Na channel’ was introduced to describe the mechanism involved in this conductance change (Hodgkin & Keynes, 1955).