Molecular weight profile of fat globule membrane proteins.

Fat globule membrane material, isolated by churning cream that had been washed four times, was extracted sequentially with .6 M potassium chloride and centrifuged to yield pellet and supernatant fractions. Compositional data indicated that lipid components were removed preferentially into the supernatant fractions. Electropherograms of the pellet and supernatant fraction in 10% and 5% sodium dodecyl sulfate-containing polyacrylamide gels revealed that the protein species originally present in the membrane associated into higher molecular weight species concomitant with the removal of lipid moieties. Thus, a contribution of the lipid moiety to membrane integrity is suggested. Approximately 17 protein-stained zones, ranging in molecular weight from 13,500 to 208,000 daltons, were observed in gels of the membrane material.