Fractionation of liver plasma membranes prepared by zonal centrifugation.

TLDR: Plasma membranes isolated from crude nuclear sediments from mouse and rat liver by a rate-dependent centrifugation through a sucrose density gradient contained in the ;A' type zonal rotor were characterized enzymically, chemically and morphologically and the heavy subfraction was found to be vesicular.

Abstract: 1. Plasma membranes were isolated from crude nuclear sediments from mouse and rat liver by a rate-dependent centrifugation through a sucrose density gradient contained in the ‘A’ type zonal rotor. 2. The membranes were further purified by isopycnic centrifugation, and characterized enzymically, chemically and morphologically. 3. When the plasma-membrane fraction of sucrose density 1.17g/cm 3 was dispersed in a tight-fitting homogenizer, two subfractions of densities 1.12 and 1.18 were obtained by isopycnic centrifugation. 4. The light subfraction contained 5′-nucleotidase, nucleoside diphosphatase, leucine naphthylamidase and Mg 2+ -stimulated adenosine triphosphatase activities at higher specific activities than unfractionated membranes. The heavy subfraction was deficient in the above enzymes but contained higher Na + +K + -stimulated adenosine triphosphatase activity. 5. The light subfraction contained twice as much phospholipid and cholesterol, and three times as much N -acetylneuraminic acid relative to unit protein weight as the heavy subfraction. Polyacrylamide-gel electrophoresis indicated differences in protein composition. 6. Electron microscopy showed the light subfraction to be vesicular. The heavy subfraction contained membrane strips with junctional complexes in addition to vesicles.