The measurement of the relative turnover rates of proteins of the surface membranes and other fractions of Schistosoma mansoni in culture.

The double isotope labelling method of Arias, Doyle & Schimke (1969) and Dehlinger & Schimke (1971) was used to determine the relative rates of turnover of proteins in various tissue fractions and in the culture medium of adult Schistosoma mansoni. The majority of proteins in the surface membrane turned over at about the same rate. This is consistent with a model for membrane assembly and degradation involving multi-protein units. The proteins in the other fractions examined, except frozen-thawed supernatant fluid, also turned over at about the same rate. In the frozen and thawed supernatant fluid, the higher molecular weight (greater than 40 000 daltons) proteins turned over at a much greater rate than the lower molecular weight proteins (less than 40 000 daltons). The antigens in the culture medium, both particulate and soluble, had a higher turnover rate than the worm tissue proteins. It is concluded that the culture medium antigens are released as the result of two distinct processes: (a) surface membrane turnover and (b) a rapid secretory process. It is possible that the high molecular weight proteins found in the forzen-thawed supernatant fluid are involved in the rapid secretory process. The culture media of 6-day and 16-day schistosomula were also examined by the double isotope method. The culture medium of the adult worm and 16-day schistosomula contains more material presumed to be secreted than does that from the 6-day schistosomula. This may explain the poor immunogenicity of young schistosomula.