Protein tyrosine kinase activity in human malaria parasite <i>Plasmodium falciparum</i>

Abstract

Protein tyrosine kinases (PTKs) are believed to be implicated in the parasite growth, maturation and differentiation functions. Protein tyrosine kinase activity was found to be distributed in all the stages of <i>P. falciparum </i>parasite maturation. Membrane bound PTK activity was found to be increased during maturation process (ring stage to trophozoite stage) in chloroquine sensitive strains. <i>In vivo </i>conversion of the schizont stage to ring stage <i>via </i>release of merozoites was associated with a decrease in PTK activity. Chloroquine inhibited the membrane bound PTK activity in a dose dependent manner (IC₅₀ = 45 μ<i>M</i>). Kinetic studies show that chloroquine is a competitive inhibitor of PTK with respect to peptide substrate and noncompetitive with respect to ATP indicating that chloroquine inhibits PTK activity by binding with protein substrate binding site. The results suggest that maturation of malaria parasite is related to PTK and inhibition of this activity by chloroquine could provide a hypothesis to explain the mechanism of action of chloroquine.