Characterization of the membrane fraction isolated by the fluorescein mercuric acetate technique of Barland and Schroeder.

Using scanning electron microscopy we have demonstrated that tha membrane fraction isolated by the fluorescein mercuric acetate technique of Barland and Schroeder (Barland, P. and Schroeder, E.A. (1975) J. Cell Biol. 45, 662-668) represents a topologically distinct membrane which circumscribes the cell nucleus. Our data suggest that not all the cells within a non-synchronized cell population release a membrane fraction after treatment according to the technique of Barland and Schroeder, but rather that the efficiency of membrane release achieved using this preparative technique is dependent on the morphology of individual cells. Our work has also demonstrated that the peptide composition of the membrane fraction isolated by the technique of Barland and Schroeder differs from the peptide composition of the plasma membrane-enriched fraction isolated by the technique of Brunette and Till (Brunette, D.M. and Till, J.E. (1971) J. Membrane Biol. 5, 215-224). This difference in peptide composition is particularly noticeable among the higher molecular weight proteins, glycoproteins and iodineateable membrane components. The data which we have accumulated suggest that the compositional differences noted between the two membrane isolates do not result from differential extraction of membrane components during the ZnCl2-fluorescein mercuric acetate treatments required in the isolation technique originally described by Barland and Schroeder. However, our data do clearly demonstrate that the membrane isolation technique of Barland and Schroeder cannot be used to study the general composition of the plasma membrane.