A group of inactivators of cysteinyl proteinases which function by covalent bond formation have been examined for their ability to inhibit thedevelopment of Plasmodium falciparum within red blood cells. The most effective of these caused inactivation of the parasite near 10−8 M concentration. The range of inhibitory action varied with peptide structure in a manner characteristic of affinity labels for proteinases suggesting that the target of inhibition was an unidentified proteinase, probably of the cysteinyl type, but different from cathepsins B and L.
