Solubilization of Spiroplasma citri cell membrane proteins with the anionic detergent sodium lauroyl-sarcosinate...

1. Up to 90 per cent of the membrane proteins from Spiroplasma citri could be solubilized with the anionic detergent Sarkosyl (sodium lauroyl-sarcosinate). Maximal solubilization was obtained with 6 to 20 mumoles of of detergent per mg of membrane protein. The insoluble residue, comprising about 10 per cent of the membrane protein, contained mainly the protein spiralin, which is quantitatively the major one of this membrane. 2. Mg2+ ions completely prevented solubilization of the membrane proteins at a molar ratio of MgCl2/Sarkosyl greater than 0.5. 3. The selectivity of Sarkosyl was also tested at low detergent concentrations and in the presence of Mg2+ ions. Spiralin was the least soluble protein also under these conditions. Other proteins were not selectively solubilized. 4. An electrophoretical and immunoelectrophoretical approach was used to study the interaction between Sarkosyl and membrane proteins. The results indicated that Sarkosyl should be considered as a mild detergent which usually solubilizes membrane proteins without gross donformational changes. This hypothesis was supported by experiments with a membrane-bound enzyme in the presence of Sarkosyl.