Protein composition and protein synthesis in the surface membranes of Schistosoma mansoni.

Abstract

Saponin treatment of cercariae and schistosomula alters the surface membrane so that it may be sheared from the organism and isolated as fragments by centrifugation. Saponin-calcium chloride treatment or freezing and thawing of adult worms removes the surface membrane, which can be washed from the bodies and collected by centrifugation. The small quantities of material available necessitated the development of a sensitive technique for detecting the proteins in the membranes. The surface membranes were radioiodinated after butan-1-ol extraction and electrophoresed in polyacrylamide gel. Adult surfaces prepared by the saponin-calcium chloride and by the freezing and thawing technique had identical protein components, detected as gel-cut profiles or in autoradiographs. The quantity of a rapidly migrating PAS-positive amido black negative component was greater in the surfaces prepared by saponincalcium chloride than in the frozen and thawed surfaces. This component contains lipid, some of which may be glycolipid. It was largely absent from the surface membranes of cercariae and schistosomula. Cercarial surface membranes contained a major protein component which was absent from the surface membranes of schistosomula. Otherwise the surface membranes of the cercariae were identical to those of the schistosomula in their protein components. The rate of incorporation of freshly synthesized protein per unit area of surface membrane of schistosomula was very low in the first 5 days in culture, after which there was a very rapid increase to a maximum rate on the 15th day. After this time, the rate of protein synthesis decreased to a low level at 26 days. In these studies the activity per unit area was measured and this would not be expected to vary greatly during growth. The biological significance of the observed variation in protein incorporation into the membrane is unclear.