Ornithine decarboxylase of Plasmodium falciparum: a peak-function enzyme and its inhibition by chloroquine.

Ornithine decarboxylase of Plasmodium falciparum shows the characteristics of a peak-function enzyme with a 20-fold increase in specific activity of the mid-late-stage trophozoites. alpha-Methylornithine inhibits the enzyme competitively, while alpha-difluoromethylornithine apparently binds irreversibly to the enzyme. The differences of the inhibitory effect on ornithine decarboxylase by chloroquine observed in intact cells and the enzyme preparation of the cell extract indicate a particular mechanism of a regulation of the enzyme.