Particles and pits matched in native membranes

Abstract

We have obtained high resolution electron microscopic images of complementary membrane surface replicas of purified microsomal vesicles from pig kidney outer medulla containing Na⁺, K⁺‐ATPase. Ultra‐rapid freezing of a membrane suspension was followed by fracturing and replicating of the liquid helium cooled specimen under ultra‐high vacuum conditions free of hydrocarbon contaminants. The protoplasmic fracture faces are populated with intra‐membrane particles while the external fracture faces reveal complementary pits. This is the first demonstration of extended precise matching of individual intramembrane particles and their corresponding pits in biological membranes containing transmembrane proteins. The data are also consistent with the theory that the majority of Na⁺, K⁺‐ATPase mass is located at the protoplasmic half of the membrane.