STUDIES ON PLASMA MEMBRANES .8. EFFECTS OF SODIUM DEOXYCHOLATE AND DODECYL SULFATE ON ISOLATED RAT-LIVER PLASMA MEMBRANES

1. 1. Plasma membranes were isolated from rat liver and dissolved in sodium deoxycholate (1%) or dodecyl sulfate (0.4 or 0.8%). Differences in the effects of the detergents on the membranes were observed. 2. 2. Analytical ultracentrifugation showed the presence of heterogeneous membrane material. The aggregation and precipitation of the solubilized membrane material by dialysis appeared to depend on the nature of the detergent used for dissolving the membranes, and the pH and ionic composition of the dialysis fluid. 3. 3. The amount of detergent bound to the dissolved membrane material after treatment with excess detergent solution was determined by three independent techniques based on a similar experimental approach, and a reasonable accordance of results was obtained. The extent of binding appeared to be a function of the detergent concentration and to exhibit an optimum. Dialysis virtually removed the detergents from the membrane material. 4. 4. Density-gradient centrifugation in a three-layer system showed a high degree of dissociation between membrane proteins and phospholipids, both in the presence of detergent and after its prior removal by dialysis. Ultrasonic irradiation also resulted in dissociation. These results were corroborated by equilibrium centrifugation in the analytical ultracentrifuge in a medium of d 1.17, and, in the case of membrane solutions from which deoxycholate had been removed, also by the capacity of the membrane material present in the individual layers of the density gradient after centrifugation to precipitate at pH 5.4. 5. 5. The results are discussed in relation to the problem of lipoprotein subunits in membranes, and the conclusion reached is that the present and other experiments with detergents do not yield evidence for the occurrence of such a structure in the plasma membrane. Criteria for judging whether the original membrane structure is restored in 'membranes' reconstructed from their constituting components are presented on account of certain properties of membrane precipitates obtained from deoxycholate solution at pH 5.4. © 1969.