Structure, isolation, and protein composition of the pellicle of Sarcocystis muris cystozoites (Protozoa, Coccidia).

The molecular organization of the Sarcocystis muris cystozoite pellicle has been investigated by freeze-fracture electron microscopy and by electrophoresis of the proteins of isolated pellicles. Freeze-fracture revealed a highly ordered organization of the inner membrane complex similar to the one described in other coccidian zoites. Purification of pellicles was achieved by French Press homogenization followed by sucrose gradient floatation. Electron microscopy of the pellicle fraction demonstrated the partial preservation of the triple-membrane structure whereas freeze-fracture showed the disorganization of the particle arrangements of the inner membrane complex. The SDS-PAGE of the fraction revealed a complex protein composition with one major protein of 31,000 daltons, not labeled by lactoperoxidase-catalyzed surface iodination of living cystozoites.