Molecular Organization fo Cell Membranes Isolated from Myxamoebae of Cellular Slime Mold, Dictyostelium discoideum

I. Presence of Membrane Subunits and the Physical Properties

Abstract

The isolation method of cell membrane of vegetative myxamoebae of Dictyoslelium discoideum is described.
The isolated cell membrane was morphologically pure with the thickness of 70-90Å, and composed of 65-70% of dry weight of protein and 25-30% of lipid.
Isolated cell membrane was dissolved completely into structural units in alkaline pH of above 11 as well as in solutions which contained detergents, urea or acetic acid. The nature of the structural unit was investigated mainly with sedimentation and electron microscopy. Lipid-free protein fraction was also dissolved in 0.1M NaOH.
The structural unit was a lipoprotein particle of which the molecular weight was about 160, 000 and had a sedimentation coefficient of 7S. This particle seemed to be globular with a diameter of 70-100Å. Lipid-free protein fraction showed a single peak in sedimentation and electrophoresis. The sedimentation coefficient was 3.3S and the molecular weight was about 65, 000.
An intermediate filamentous structure, which was a linear aggregate of 7S subunits, appeared in the process of degrading the membrane into particles in an alkaline solution.