76 BIOCHIMICA ET BIOPHYSICA ACTA BBA 75 6ox ELECTRON MICROSCOPY OF SOLUBILIZED ACHOLEPLASMA LAIDLAWII MEMBRANE PROTEINS REAGGREGATED WITH MYCOPLASMA PNEUMONIAE GLYCOLIPIDS R. M. COLE, T. J. POPKIN, B. PRESCOTT, R. M. CHANOCK AND S. RAZIN* Laboratory of Microbiology and Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md. 2ooi 4 (U.S.A.) (Received October I9th, 197 o) SUMMARY I. The purified glycolipid haptens of Mycoplasma pneumoniae were reaggregated with Acholeplasma laidlawii membrane proteins. The process consisted of the solubili- zation of lipid-depleted A. laidlawii membranes and M. pneumoniae glyeolipids in 2o mM sodium dodecyl sulfate, and dialysis of the solution separately or in mixtures against 2o mM Mg 2+. 2. The reaggregated material collected by centrifugation of the dialyzed solution of lipid-depleted A. laidlawii membrane proteins consisted of amorphous clumps, while the reaggreated M. pneumoniae glycolipids consisted of "myelin-like" globules and sheets composed of lamellae with a mean center-to-center distance of 37 A. The reaggregated material of a mixture of lipid-depleted A. laidlawii membrane proteins and M. pneumoniae glycolipids contained, in addition to the amorphous clumps representing reaggregated proteins and the "myelin-like" structures re- presenting reaggregated glycolipids, also long membranous sheets having a triple- layered structure with a mean center-to-center distance of the dense lines of 54 A. The appearance and dimensions are closely similar to those of the original or reagre- gated A. laidlawii membranes. 3. It is suggested that these membrane-like structures are formed by the asso- ciation of A. laidlawii membrane protein and M. pneumoniae glycolipids, and that these "hybrid" structures are responsible for the increased antigenicity of the re- aggregated glycolipids. INTRODUCTION Sodium dodecyl sulfate has been shown to solubilize mycoplasma membranes to separate protein-detergent and lipid-detergent micelles1,2. In spite of the complete separation of the protein from the lipid by sodium dodecyl sulfate, these components could reaggregate spontaneously to form typical triple-layered membranes on removal of the detergent by dialysis against a Mg2+-containing buffer~-4. Further * Visiting Scientist on leave from the Hebrew University, Hadassah Medical School, Jerusa- lem, Israel, Biochim. Biophys. Acta, 233 (i97 I) 76-83