LIPOSOME SOLUBILIZATION AND MEMBRANE-PROTEIN RECONSTITUTION USING CHAPS AND CHAPSO

The processes of liposome solubilization and reconstitution of two tra nsport proteins have been studied using Chaps and Chapso -[(3-cholamid opropyl)dimethylammonio]-2-hydroxy-1- propanesulfonate). The solubiliz ation of unilamellar liposomes was followed by absorption experiments and the process was shown to fit well to the three-stage model previou sly proposed for other detergents, The solubilization parameters have been determined and the detergent to phospholipid ratios at which the lamellar-to-micellar transition initiates and ends were estimated to b e 0.21 mol/mol and 0.74 mol/mol, for Chapso and 0.4 mol/mol and 1.04 m ol/mol for Chaps, respectively. The best conditions for the incorporat ion of two membrane proteins, bacteriorhodopsin and the H+-ATP synthas e from chloroplasts, were analyzed at each step of the solubilization process. After detergent removal, the activities of the resulting prot eoliposomes were measured indicating that the most efficient reconstit utions were obtained by addition of the proteins to completely solubil ized lipid-detergent micelles. The use of Chapso and Chaps far membran e protein reconstitution studies provides a reproducible method of ach ieving active proteoliposomes, homogeneous in size, with a low permeab ility and thus, well suited for transport measurements.