Nitric oxide inhibits falcipain, the Plasmodium falciparum trophozoite cysteine protease

Nitric oxide (NO) is a pluripotent regulatory molecule possessing, among others, an antiparasitic activity. In the present study, the inhibitory effect of NO on the catalytic activity of falcipain, the papain-like cysteine protease involved in Plasmodium falciparum trophozoite hemoglobin degradation, is reported. In particular, NO donors S-nitrosoglutathione (GSNO), (±)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-n-3-hexenamide (NOR-3), 3-morpholinosydnonimine (SIN-1), and sodium nitroprusside (SNP) inhibit dose-dependently the falcipain activity present in the P. falciparum trophozoite extract, this effect likely attributable to S-nitrosylation of the Cys25 catalytic residue. The results represent a new insight into the modulation mechanism of falcipain activity, thereby being relevant in developing new strategies for inhibition of the P. falciparum life cycle. (C) 2000 Academic Press.