Chemical characterization of the proteins and glycoproteins of mouse liver plasma membranes solubilized by sequential extraction with aqueous and organic solvents.

1. A procedure for the stepwise fractionation of the proteins of mouse liver plasma membranes is described. 2. Of the membrane protein 20-25% was soluble in 50mm-sodium carbonate-bicarbonate buffer (pH9.7). This fraction contained a large number of proteins but only 1 major glycoprotein. It was low in sialic acid, amino sugars and phospholipid. 3. Extraction of the alkali-insoluble residue with aq. 33% pyridine solubilized an additional 30-35% of the membrane protein. The pyridine-soluble membrane components were enriched in sialic acid and glucosamine and it was shown that this procedure resulted in the selective extraction of glycoproteins. 4. Gel filtration in sodium dodecyl sulphate resolved the pyridine-soluble proteins into five fractions of decreasing molecular weight and an inverse relationship between molecular weight and sialic acid content was indicated.