EVALUATION OF THE EFFICACY OF ZWITTERIONIC DODECYL CARBOXYBETAINE SURFACTANTS FOR THE EXTRACTION AND THE SEPARATION OF MYCOPLASMA MEMBRANE-PROTEIN ANTIGENS

The ability to extract mycoplasma membrane protein antigens using the alkyl carboxybetaine surfactants (N-dodecyl-N,N-dimethylammonio)butyra te (DDMAB, CMC = 4.3 mM) and (N-dodecyl-N,N-dimethylammonio)undecanoat e (DDMAU, CMC 0.13 mM) was assessed by protein titration and SDS-PAGE analysis. The maximum yields of membrane protein solubilization ranged from 20 to 90%, depending upon both the mycoplasma membrane investiga ted and the surfactant used. In five of six cases, the extraction was optimal for surfactant concentrations of ca. 25 mM. DDMAB displayed a higher efficiency in membrane protein extraction. The order of efficie ncy for both surfactants was Spiroplasma melliferum > Acholaplasma lai dlawii > Mycoplasma gallisepticum. In contrast, DDMAU proved much more selective. The order of selectivity was M. gallisepticum > S. mellife rum > A. laidlawii. The highest selectivity was recorded for the major proteins p67 and spiralin of M. gallisepticum and S. melliferum, resp ectively, For p67, notably, DDMAU proved superior to 10 other surfacta nts. Dot immunobinding and crossed immunoelectrophoresis analyses show ed that both dodecyl carboxybetaines were suitable as membrane protein -solubilizing agents in immunological techniques. Furthermore, these s urfactants did not exhibit effects adverse to the activity of A. laidl awii membrane NADH oxidase. One promising application of DDMAU is the separation of membrane proteins by ion-exchange HPLC as illustrated by the good resolution of M. gallisepticum membrane proteins and purific ation of p67 to almost homogeneity. These data show that dodecyl carbo xybetaine surfactants are useful for the extraction of mycoplasma memb rane antigens under mild conditions. Their mildness toward proteins wa s attributed to their zwitterionic characteristics, whereas the select ivity of DDMAU was due to the longer polymethylene intercharge arm in this molecule (10 vs 3 methylenes for DDMAB). (C) 1995 Academic Press, Inc.