Isolation and Characterization of Surface Antigens from Schistosoma mansoni. I. Evaluation of Techniques for Radioisotope Labeling of Surface Proteins from Adult Worms

Radiolabeled surface proteins of adult Schistosoma mansoni were prepared by in vitro labeling of whole worms, and by labeling freeze-thaw surface membrane extracts. Incorporation of 125I into surface proteins was attempted using the lactoperoxidase, chloramine-T, iodosulfanilic acid, and Bolton-Hunter methods. Radiolabeling of whole worms with lactoperoxidase, chloramine-T and iodosulfanilic acid yielded a single protein peak (mol wt > 100,000) on SDS-PAGE, and showed considerable incorporation of label in the lipid fraction. Bolton-Hunter labeling of whole worms yielded four major peaks with molecular weights of 100,000, 60,000, 30,000 and 21,000, and minor peaks with molecular weights of 26,000, 36,000, 43,000, 68,000 and 78,000; three of the four major peaks corresponded to prominent bands in Coomassie blue-stained gels. Although carbohydrate-labeling techniques were not successful, a single carbohydrate band, molecular weight > 100,000, was detected with PAS staining. Radiolabeling of freeze-thaw extracts yielded results similar to those obtained with whole worms. Electron microscopy revealed the tegument to be left intact and undamaged after labeling with the Bolton-Hunter reagent.