Sarcocystis muris (Apicomplexa): a thiol protease from the dense granules.

Homogenates of Sarcocystis muris merozoites (cyst form) and the subcellular fraction of dense granules were assayed for protease activity with substrate-impregnated SDS-polyacrylamide gels. Four acidic and several basic proteases were detected in the merozoites. One of the basic proteases was further characterized as a thiol protease (EC 3.4.22). The activity of this protease was enriched in the dense granule fraction.