Isolation and characterization of the plasma membrane from Yoshida hepatoma cells

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Abstract
Plasma membranes isolated from Yoshida ascites hepatoma AH-130 by a modification of the method of T. K. Ray (Biochim. Biophys. Acta 196: 1, 1970), were subfractionated into three fractions having densities (d) 1.12, 1.14 and 1.16 by discontinuous sucrose density-gradient. Membrane subfractions were characterized by electron-microscopy, by assay of marker enzymes and by lipid composition. All subfractions appeared to be essentially free from whole mitochondria, lysosomes and nuclei. Subfraction d 1.16 had, the highest 5′-nucleotidase, Mg++-ATPase and (Na++K+)-ATPase activities; cytochromec oxidase was undetectable in any fraction and glucose-6-phosphatase was measurable only in fraction d 1.14. Adenylate cyclase had the highest activity in fractions d 1.14 and 1.16. Cyclic AMP phosphodiesterase was nearly equally distributed in the fractions. Adenylate, cyclase, 5′-nucleotidase and Mg++-ATPase activities of tumor membrane were lower with respect to liver plasma membrane, while cyclic AMP phosphodiesterase and (Na++K+)-ATPase were found to have similar activities in the two membrane preparations. With respect to liver membrane, hepatoma membrane contained a higher amount of glycolipids and a higher amount of phospholipids accounted for mainly, by sphingomyelin, phosphatidylserine and phosphatidic acid. The possible significance of the decrease of adenylate activity in the hepatoma membrane is briefly discussed.