Sharma Arun, Biswas Sukla
Department of Protein Biochemistry, Malaria Research Centre, 22 Sham Nath Marg, Delhi 110 054, India.
Indian J Biochem Biophys. 2005 Jun;42(3):145-51.
Protein kinase C (PKC)-like activity was characterized in malarial parasite Plasmodium falciparum and its involvement in growth, maturation and differentiation functions, during the asexual stages (ring, trophozoite and schizont) of development was studied. PKC-like activity was found distributed in all the stages of the parasite maturation. The activity was predominantly cytosolic, however it was also present in the membrane fraction. The activation of cytosolic PKC required Ca2+, phosphatidyl serine (PS), and either diacylglycerol or phorbol myristate acetate (PMA). The 9-fold increase in the activity was observed in the presence of the co-factors (Ca2+, PS and PMA) in the late trophozoite stage, as compared to the ring stage. The activation of trophozoites with PMA resulted in redistribution of PKC-like activity from cytosol to membrane fractions. An antimalarial drug, chloroquine (CQ) inhibited directly the PKC-like activity in a dose-dependent manner (IC50 of 45 nM) in trophozoites of chloroquine-sensitive CQ(S) strains, however, the activity remained unaltered in the chloroquine-resistant CQ(R) strains. Kinetic studies showed that the inhibition of cytosolic PKC-like activity by CQ was non-competitive with respect to ATP, histone and PS. The results suggest that the PKC-like activity is developmentally expressed during the parasitic survival and development.
在恶性疟原虫中鉴定出了蛋白激酶C（PKC）样活性，并研究了其在无性发育阶段（环状体、滋养体和裂殖体）参与生长、成熟和分化功能的情况。发现PKC样活性分布于寄生虫成熟的所有阶段。该活性主要存在于胞质中，但也存在于膜组分中。胞质PKC的激活需要Ca2+、磷脂酰丝氨酸（PS）以及二酰基甘油或佛波酯肉豆蔻酸酯（PMA）。与环状体阶段相比，在滋养体后期阶段，在存在辅助因子（Ca2+、PS和PMA）的情况下观察到活性增加了9倍。用PMA激活滋养体导致PKC样活性从胞质重新分布到膜组分中。一种抗疟药物氯喹（CQ）以剂量依赖性方式直接抑制氯喹敏感CQ（S）株滋养体中的PKC样活性（IC50为45 nM），然而，在氯喹耐药CQ（R）株中该活性保持不变。动力学研究表明，CQ对胞质PKC样活性的抑制相对于ATP、组蛋白和PS是非竞争性的。结果表明，PKC样活性在寄生虫存活和发育过程中呈发育性表达。
