Adsorption of proteins from the Spiroplasma citri cell membrane by magnesium lauroyl-sarcosinate crystals.

Interactions between the ionic detergent Sarkosyl (sodium lauroyl sarcosinate), Mg2+ ions, and the Spiroplasma citri cell membrane were analyzed microscopically and electrophoretically. Studies were performed under conditions where membrane proteins were apparently not released from the membrane by the detergent (molar ratio of MgCl2/Sarkosyl = 0.5). Although the S. citri membrane interfered with the crystallization phenomenon to some extent, the formation of Sarkosyl-Mg2+ crystals occurred regardless to the sequence of addition of the three components. Concomitantly the structure of the membrane disintegrated and membrane components were adsorbed to the crystal surfaces. The membrane protein fraction bound to the crystals was composed of the majority of the putatively intrinsic polypeptides, including the amphiphilic protein spiralin, and several extrinsic polypeptides. The polypeptide compositions of M-bands (crystal fractions loaded with membrane material) prepared from S. citri cells and from isolated S. citri membranes were similar, as shown by sodium dodecyl-sulfate electrophoresis and crossed immunoelectrophoresis. These results show that, the S. citri cell membrane, in contrast to bacterial membranes, is not protected from the effect of Sarkosyl by Mg2+ ions.