An analysis of fumarate reductase systems in parasitic helminths and various intermediate molluscan hosts

一些寄生蠕虫和水生软体动物主要通过磷酸烯醇-丙酮酸羧激酶（PEPCK）-琥珀酸途径利用葡萄糖;这是碳水化合物代谢的替代途径，琥珀酸是最终产物之一。该途径的最终步骤是延胡索酸还原反应，该反应由线粒体电子传递酶催化，其中延胡索酸作为电子受体发挥作用。延胡索酸还原酶系统产生ATP，本项目对不同环境下的猪蛔虫、卫氏并殖吸虫和软体动物中间宿主的延胡索酸还原酶系统进行了比较研究，以了解其生理意义。本实验室的前期研究表明，蛔虫和并殖吸虫成虫线粒体中的一种B型细胞色素参与了延胡索酸还原酶系统，该细胞色素可与复合体III中的B型细胞色素区分开来。在该项目的过程中，b型细胞色素，B_<558>用于蛔虫或 ...更多信息 B_<556>（并殖吸虫）在复合体Ⅱ分离程序建立后，发现定位于蠕虫呼吸链的复合体Ⅱ中。蛔虫细胞色素B_的中点氧化还原电位（Em）<558>为-34 mV。牛心肌线粒体复合体II中存在类似的b型细胞色素，但其Em更负（-185 mV）。寄生虫复合体II中的b型细胞色素容易被琥珀酸盐还原，但牛心复合体II中的情况并非如此。蛔虫和并殖吸虫的复合物II与牛心复合物一样，由四个亚基组成。利用高效液相色谱法研究表明蛔虫细胞色素B<558>_对应于两个较小的亚基。复合物II的最大亚基的分子特性在所有三个物种之间是相似的，它们的免疫同源性高。然而，这两个较小的亚基具有不同的性质，具有可忽略的免疫同源性。蛔虫复合物II具有较高的延胡索酸还原酶活性。此外，一个NADH-延胡索酸还原酶活性重建与牛心复合物I，蛔虫复合物II和玫瑰醌，表明醌是一个重要组成部分的NADH-延胡索酸还原酶系统。至于中间软体动物宿主的研究，厌氧浸泡实验，这是在灭螺剂的存在下进行的，然后分析有机酸，显示PEPCK-琥珀酸途径是在体内的功能在钉螺和光滑双脐螺。少

Some parasitic helminths and aquatic molluscs utilize glucose mainly through a phosphoenol-pyruvate carboxykinase(PEPCK)-succinate pathway; an alternative pathway of the carbohydrate metabolism with succinate as one of the resulting end-products. The terminal step of the pathway is a fumaratereducing reaction, which is catalyzed by mitochondrial electron transport enzymes and where fumarate functions as an electron acceptor. The fumarate reductase system produces ATP.In this project, fumarate reductase systems of Ascaris suum, Paragonimus westermani and molluscan intermediate hosts, which inhabit in various environments, were comparatively studied to understand their physiological significance. Previous study in our laboratory showed that a type b cytochrome, which can be distiguished from b cytochromes in complex III, participated in the fumarate reductase system in Ascaris and Paragonimus adult mitochondria. In the course of the project, the b-type cytochrome, b_<558> for Ascaris or … More b_<556> for Paragonimus, was found to be localized in complex II of the worm respiratory chain after the procedure for isolation of complex II had been established. The midpoint oxidation-reduction potential (Em) of Ascaris cytochrome b_<558> was - 34 mV. A similar b-type cytochrome exists in complex II of beef heart mitochondria though its Em is more negative (-185 mV). The b-type cytochrome in parasite complex II was easily reduced by succinate but it was not the case in beef heart complex II. Complexes II, of Ascaris and Paragonimus, were composed of four subunits like beef heart one. Studies using high performance liquid chromatography showed Ascaris cytochrome b_<558> tocorrespond to the two smaller subunits. Molecular properties of the largest subunit of complex II were similar among all three species and their immunological homology was high. However, the two smaller subunits had different properties with negligible immunological homology. Ascaris complex II had a high fumarate reductase activity. Also, an NADH-fumarate reductase activity was reconstituted with beef heart complex I, Ascaris complex II and rhodoquinone, indicating the quinone to be an essential component of the NADH-fumarate reductase system. As to studies on intermediate molluscan hosts, anaerobic immersion experiments, which were performed in the presence of molluscicides and followed by analyses of organic acids, showed the PEPCK-succinate pathway to be in function in vivo in Oncomelania nosophora and Biomphalaria glabrata snails. Less