The characterization of actin associated with postsynaptic membranes from Torpedocalifornica

SDS-polyacrylamide gel electrophoresis of acetylcholine receptor from $\text{Torpedo}\text{californica}$ electroplax membrane fragments shows, in addition to the four receptor subunits of 40,000, 50,000, 60,000 and 65,000 daltons, other components of apparent molecular weights 43,000, 47,000 and 90,000 daltons. In this study deoxyribonuclease I inhibitory activity has been used to identify actin in $\text{Torpedo}\text{californica}$ receptor-enriched membranes and affinity chromatography on a deoxyribonuclease I agarose column has been used to purify this protein from the membrane preparations. In addition the membrane protein components have been analyzed by electrophoresis on a series of SDS-polyacrylamide gels of varying acrylamide concentrations. Evidence is presented that actin is a component of most preparations of receptor-enriched membrane fragments, having an apparent molecular weight of 47,000 daltons, and is distinct from the 43,000 dalton protein.