Atamna H, Ginsburg H
Department of Biological Chemistry, Hebrew University, Jerusalem, Israel.
Mol Biochem Parasitol. 1993 Oct;61(2):231-41. doi: 10.1016/0166-6851(93)90069-a.
Oxidative radicals are demonstrably produced in malaria-infected erythrocytes. In order to verify the biochemical origin of these radicals, erythrocyte lysate was brought to acid pH to mimic the environment of the parasite food vacuole into which host cell cytosol is transferred during parasite feeding. Oxyhemoglobin, but not deoxyhemoglobin, is rapidly converted to methemoglobin at rates which decline with increasing pH. The rate of conversion is further increased in the presence of the catalase inhibitor 3-amino-1,2,4-triazole (3-AT) and the extent of inhibition of the lysate catalase increases upon acidification, implying that H2O2 is thus produced by the spontaneous dismutation of superoxide radicals generated during methemoglobin formation. Intact Plasmodium falciparum trophozoite-infected human red blood cells (TRBC) were shown to produce H2O2 and OH radicals about twice as much as normal erythrocytes, as evidenced by the inhibition of endogenous catalase activity in the presence of 3-AT and the degradation of deoxyribose, respectively. Increased H2O2 levels and catalase activity were found in both host cell and parasite compartments. No increase in H2O2 production over that observed in uninfected erythrocytes could be detected at the ring stage when host cell digestion is absent. H2O2 and OH radicals production in TRBC was considerably reduced when digestion of host cell cytosol was inhibited either by antiproteases (which reduce the proteolysis of imported catalase) or by its alkalinization with NH4Cl (which reduce methemoglobin formation). These results suggest that reactive oxygen species are produced in the parasite's food vacuole during the digestion of host cell cytosol, and are able to egress from the parasite to the host cell compartment.
氧化自由基在感染疟原虫的红细胞中明显产生。为了验证这些自由基的生化来源，将红细胞裂解物调至酸性pH值，以模拟寄生虫食物泡的环境，在寄生虫摄取营养期间，宿主细胞胞质溶胶会转移到该食物泡中。氧合血红蛋白而非脱氧血红蛋白会迅速转化为高铁血红蛋白，其转化速率随pH值升高而下降。在过氧化氢酶抑制剂3-氨基-1,2,4-三唑（3-AT）存在的情况下，转化速率进一步提高，并且酸化后裂解物过氧化氢酶的抑制程度增加，这意味着高铁血红蛋白形成过程中产生的超氧自由基自发歧化会产生H2O2。完整的恶性疟原虫滋养体感染的人类红细胞（TRBC）产生的H2O2和OH自由基大约是正常红细胞的两倍，分别通过在3-AT存在下内源性过氧化氢酶活性的抑制和脱氧核糖的降解得以证明。在宿主细胞和寄生虫区室中均发现H2O2水平和过氧化氢酶活性增加。在环状体阶段，由于不存在宿主细胞消化，未检测到H2O2产生量比未感染红细胞中的增加。当宿主细胞胞质溶胶的消化受到抗蛋白酶（其减少导入的过氧化氢酶的蛋白水解）或用NH4Cl碱化（其减少高铁血红蛋白形成）的抑制时，TRBC中H2O2和OH自由基的产生会显著减少。这些结果表明，活性氧在宿主细胞胞质溶胶消化期间在寄生虫的食物泡中产生，并能够从寄生虫逸出到宿主细胞区室。
