Selective solubilization with tween 20 of membrane proteins from Acholeplasma laidlawii

Abstract

1. 1. Approx. 70% of the plasma membrane from Acholeplasma laidlawii can be extracted with 2.5% Tween 20. The residue contained a higher proportion of hydrophobic amino acids than the extract. Glucosamine and galactosamine were found only in the extract. The extraction with Tween 20 is unusually selective: polyacrylamide-gel electrophoresis in sodium dodecyl sulfate of the extract and of the residue showed that the extract contained several membrane proteins that were absent from the residue and vice versa. 2. 2. The proteins in the Tween extract were frationated by analytical polyacrylamide-gel electrophoresis in the presence of Tween 20 into three major and two minor zones (see Fig. 6). 3. 3. A laidlawii membranes, completely solubilized in sodium dodecyl sulfate, were submitted to polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. Five major and seven minor zones were obtained. This technique also permitted a rough estimate of the molecular weights of the proteins in these twelve zones; values from 15000 to 140000 were obtained. 4. 4. The five protein zones obtained by electrophoresis in Tween 20 (see point 2 above) were further fractionated in sodium dodecyl sulfate by a two-dimensional electrophoresis procedure (see Fig. 7). 5. 5. The yellow color of the A. laidlawii membrane is due to the presence of both flavoprotein(s) and carotenoid material, the latter pigment being either in free form or in association with lipids. 6. 6. An approach to the determination of the geometric localization of components in a membrane is discussed (although not utilized in the present studies). 7. 7. The risk of misinterpretations in membrane studies due to the possible appearance of artificial complexes is discussed.