In this project we will characterize the Plasmodium falciparum cysteine protease falcipain and evaluate this enzyme as a potential target for antimalarial chemotherapy. We have previously identified falcipain as a hemoglobinase and shown that falcipain inhibitors block hemoglobin degradation and parasite development, suggesting that falcipain is an essential enzyme and logical chemotherapeutic target. The testing of falcipain inhibitors as antimalarial is ongoing. However, it is also important to better characterize the biochemical properties and biological role of this enzyme, as these data will improve our ability to design and test falcipain inhibitors. Specific aims of this project will be: (1) to characterize the biochemical properties of native and recombinant falcipain, (2) to evaluate the biological role of falcipain, and (3) to test falcipain inhibitors as potential antimalarial drugs. The project will allow us to rigorously test two hypotheses. First, we hypothesize that falcipain is an essential plasmodial hemoglobinase that is responsible for early cleavages of hemoglobin and is required for parasite development. Second, we hypothesize that falcipain inhibitors will be effective antimalarial drugs. The experiments outlined in this proposal should provide a clear characterization of the biochemical properties and biological role of falcipain. In addition, the planned evaluation of the effects of falcipain inhibitors on cultured parasites and animal models of malaria should critically test this enzyme as a chemotherapeutic target. This evaluation is also likely to identify specific falcipain inhibitors with potent antimalarial activity that will be ready for initial testing against human malaria.