A plasmodium protein kinase that is developmentally regulated, stimulated by spermine, and inhibited by quercetin

Abstract

Plasmodium berghei–infected murine red cells possess protein kinase activity that is associated with the isolated parasites. Schizonts contain significantly higher levels of this protein kinase than the more immature forms, suggesting a relationship between this enzyme activity and parasite development. Partially purified protein kinase has a K_m for ATP of ∼30 μM, whereas the K_m for GTP is ∼300 μM and the substrate preference is phosvitin > casein > > histone > protamine. The Mg²⁺ optimum is 10–20 mM, and the protein kinase activity is stimulated by the polyamines spermine and spermidine. The flavone, quercetin, inhibits the protein kinase activity in a competitive manner with' respect to ATP (Ki ∼3 μM), and P chabaudi also has a very similarly regulated protein kinase. Protein kinases from both species are very similar to the type I casein kinase.