Söderström M, Hammarström S, Mannervik B
Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, Sweden.
Biochem J. 1988 Mar 15;250(3):713-8. doi: 10.1042/bj2500713.
Leukotriene C4 synthesis was studied in preparations from mouse mastocytoma cells. Enzymic conjugation of leukotriene A4 with glutathione was catalysed by both the cytosol and the microsomal fraction. The specific activity of the microsomal fraction (7.8 nmol/min per mg of protein) was 17 times that of the cytosol fraction. The cytosol fraction of the mastocytoma cells contained two glutathione transferases, which were purified to homogeneity and characterized. A microsomal glutathione transferase was purified from mouse liver; this enzyme was shown by immunoblot analysis to be present in the mastocytoma microsomal fraction at a concentration one-tenth or less of that in the liver microsomal fraction. Both the cytosolic and the microsomal glutathione transferases in the mastocytoma cells were identified with enzymes previously characterized, by determining specific activities with various substrates, sensitivities to inhibitors, reactions with antibodies, and physical properties. The purified microsomal glutathione transferase from liver was inactive with leukotriene A4 or its methyl ester as substrate. The cytosolic enzymes displayed activity with leukotriene A4, but their specific activities and intracellular concentrations were too low to account for the leukotriene C4 formation in the mastocytoma cells. The microsomal fraction of the cells contained an enzyme distinguishable by various criteria from the previously studied glutathione transferases. This membrane-bound enzyme, leukotriene C synthase (leukotriene A4:glutathione S-leukotrienyltransferase), appears to carry the main responsibility for the biosynthesis of leukotriene C4.
在小鼠肥大细胞瘤细胞制备物中研究了白三烯C4的合成。白三烯A4与谷胱甘肽的酶促共轭反应由胞质溶胶和微粒体部分催化。微粒体部分的比活性（每毫克蛋白质7.8 nmol/分钟）是胞质溶胶部分的17倍。肥大细胞瘤细胞的胞质溶胶部分含有两种谷胱甘肽转移酶，将它们纯化至同质并进行了表征。从小鼠肝脏中纯化出一种微粒体谷胱甘肽转移酶；免疫印迹分析表明，该酶在肥大细胞瘤微粒体部分中的浓度是肝脏微粒体部分的十分之一或更低。通过测定对各种底物的比活性、对抑制剂的敏感性、与抗体的反应以及物理性质，确定肥大细胞瘤细胞中的胞质溶胶和微粒体谷胱甘肽转移酶与先前表征的酶相同。从肝脏中纯化的微粒体谷胱甘肽转移酶以白三烯A4或其甲酯作为底物时无活性。胞质溶胶酶对白三烯A4有活性，但其比活性和细胞内浓度过低，无法解释肥大细胞瘤细胞中白三烯C4的形成。细胞的微粒体部分含有一种根据各种标准可与先前研究的谷胱甘肽转移酶区分开来的酶。这种膜结合酶，白三烯C合酶（白三烯A4：谷胱甘肽S - 白三烯基转移酶），似乎对白三烯C4的生物合成起主要作用。
