Zonal density gradient electrophoresis of intracellular membranes of brain cortex.

Rat cerebral cortex was homogenized in a sucrose-free medium and a number of intracellular melnbrane fractions were isolated therefrom by means of differential and density-gradient centrifugation. The mitochondrial and microsomal membrane fractions, as well as the separated rough and smooth endoplasmic reticulum components of the latter, were subjected to zonal density gradient electrophoresis. With this technique it was possible to determine the electrokinetic profile of the melnbranes contained in each fraction. The application of zonal density gradient electrophoresis to the melnbrane populations obtained by density-gradient centrifugation revealed marked differences in electrophoretic lnobility between them which correlated directly with both their membrane-bound N-acetylneuraminie acid content and their aeetylcholinesterase (EC 3.I.I.7) activity. The fraction containing membranes in which both of these components were highest and, hence, presumably synaptic in derivation, was isolated as a single, homogeneous electrophoretic peak.