SELECTIVE REAGGREGATION OF SOLUBILIZED MYCOPLASMA-MEMBRANE PROTEINS AND KINETICS OF MEMBRANE REFORMATION

1. 1. Proteins and lipids of mycoplasma membranes solubilized in sodium dodecyl sulfate reaggregated to membraneous structures when the detergent was diluted by dialysis against a Mg2+-containing buffer. The Mg2+ concentration determined the degree of reaggregation, the lipid-to-protein ratio in the reaggregate and, as shown by electrophoretic and enzymic analyses, the species of membrane proteins aggregated. 2. 2. The reassembly of the solubilized membrane components to membraneous structures proceeded rapidly. After 40 min of dialysis against 20 mM Mg2+, the reaggregate already contained membranes of a similar triple-layered structure and thickness as the original ones, but with a smaller number of protein species and a higher lipid-to-protein ratio. 3. 3. On density-gradient analysis reaggregates of Mycoplasma laidlawii membranes were found to be heterogeneous, while at 5 mM Mg2+ only a light" lipid-rich band (d = 1.140) was obtained. At higher Mg2+ concentrations this was accompanied by one or two heavier bands. The "light" band was transformed into a heavier one when the Mg2+ concentration was increased. 4. 4. Our data suggest that the reaggregated membranes are assembled by a multi-step process and not by the single-step assembly of lipoprotein subunits. 5. 5. The application of the selective aggregation of solubilized membrane proteins to the fractionation and characterization of membrane enzymes and antigens is suggested and discussed. © 1969."