vander Jagt D L, Hunsaker L A, Campos N M, Scaletti J V
Department of Biochemistry, University of New Mexico School of Medicine, Albuquerque 87131.
Biochim Biophys Acta. 1992 Aug 21;1122(3):256-64. doi: 10.1016/0167-4838(92)90401-x.
Three hemoglobin-degrading proteinases were partially purified from food vacuoles isolated from trophozoite-stage forms of the malarial parasite Plasmodium falciparum. Two of the proteinases (M1 and M2) were solubilized by repeated sonication. The remaining proteinase (M3) was solubilized by treatment of the particulate fraction with taurocholic acid, suggesting that proteinase M3 is a membrane-bound proteinase whereas proteinases M1 and M2 are weakly associated with parasite membrane. The location of these proteinases suggests that they may participate in the digestion of host cytosolic protein. After partial purification, but not before, proteinases M1, M2 and M3 are highly sensitive to pepstatin, supporting their designation as aspartic proteinases. These aspartic proteinases show broad specificity for protein substrates. Native hemoglobin, acid denatured hemoglobin and oxidatively damaged hemoglobin are comparable substrates. Hemoglobin within the food vacuole was shown to be primarily native hemoglobin. Chemical modification studies indicate that these three aspartic proteinases have similar properties. The peptide maps from degradation of hemoglobin, however, suggest that aspartic proteinases M1, M2 and M3 are distinct proteinases.
从恶性疟原虫滋养体阶段的食物泡中部分纯化出三种血红蛋白降解蛋白酶。其中两种蛋白酶（M1和M2）通过反复超声处理而溶解。剩余的蛋白酶（M3）通过用牛磺胆酸处理颗粒部分而溶解，这表明蛋白酶M3是一种膜结合蛋白酶，而蛋白酶M1和M2与寄生虫膜的结合较弱。这些蛋白酶的定位表明它们可能参与宿主胞质蛋白的消化。在部分纯化之后而非之前，蛋白酶M1、M2和M3对胃蛋白酶抑制剂高度敏感，这支持了它们作为天冬氨酸蛋白酶的命名。这些天冬氨酸蛋白酶对蛋白质底物具有广泛的特异性。天然血红蛋白、酸变性血红蛋白和氧化损伤的血红蛋白都是类似的底物。食物泡内的血红蛋白主要显示为天然血红蛋白。化学修饰研究表明这三种天冬氨酸蛋白酶具有相似的性质。然而，血红蛋白降解产生的肽图表明天冬氨酸蛋白酶M1、M2和M3是不同的蛋白酶。
