Ultrastructure, fractionation and biochemical analysis of Cryptosporidium parvum sporozoites.

Sporozoites of the apicomplexan parasite Cryptosporidium parvum were subjected to cell disruption and subcellular fractionation using a sucrose density step gradient. With this procedure, highly enriched preparations of the parasite membrane, the micronemes, dense granules and amylopectin granules were produced. No separate fraction containing rhoptries was obtained, however this organelle was found in defined fractions of the gradient, still associated with the apical tip of the sporozoites. Using negative staining, the internal structure of the micronemes was revealed by transmission electron microscopy. Micronemes and dense granules showed characteristic protein compositions by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The micronemes contained three major proteins of approximately 30, 120 and 200 kDa and the dense granules contain five major proteins in the 120-180 kDa range.