Inhibition of ornithine decarboxylase of in vitro cultured Plasmodium falciparum by chloroquine.

Ornithine decarboxylase of P. falciparum, the initial and rate-limiting enzyme of the synthesis of polyamines, was inhibited by chloroquine when P. falciparum-infected red cells in culture were incubated in the presence of chloroquine for two hours. The degree of these inhibition produced by mefloquine was less. On the basis of these findings a sequence of reactions is discussed to define the mode of action of chloroquine. Additionally a preliminary investigation of the ornithine analogue, difluoromethylornithine, showed inhibitory effects on ornithine decarboxylase activity of P. falciparum.