Worsham L M, Williams S G, Ernst-Fonberg M L
Department of Biochemistry, James H. Quillen College of Medicine, East Tennessee State University, Johnson City 37614-0581.
Biochim Biophys Acta. 1993 Sep 29;1170(1):62-71. doi: 10.1016/0005-2760(93)90176-a.
Euglena gracilis is a very ancient eukaryote whose chloroplast acquisition and evolution has been independent of higher plants. The organism in unique in possessing two de novo fatty acid synthases, a true multienzyme complex of great size in the cytosol and a plastid-localized type II fatty acid synthase composed of discrete enzymes and acyl carrier protein (ACP). The enzymology of the early steps of fatty acid biosynthesis differed in the Euglena type II fatty acid synthase compared to those of Escherichia coli and plants. The enzymes of Euglena participating in both priming and elongation reactions to form a new carbon-carbon bond were acetyl-CoA-ACP transacylase, malonyl-CoA-ACP transacylase, and beta-ketoacyl-ACP synthase I. The effects of inhibitors on the three different enzymes were noted. All carbon-carbon bond formation was inhibited by cerulenin. Although neither fatty acid biosynthesis nor any of the isolated enzymes were sensitive to diisopropylphosphofluoridate, the three Euglena enzymes studied were sensitive to different sulfhydryl-alkylating agents. Acetyl-ACP supported fatty acid biosynthesis as effectively as did comparable amounts of ACPSH and acetyl-CoA. There was no evidence for a beta-ketoacyl-ACP synthase III for priming such as has been reported in type II fatty acid synthase of higher plants and bacteria. The roles of the acetyl-CoA-ACP transacylase and beta-ketoacyl-ACP synthase I appear to be unique in the type II fatty acid synthase of Euglena. Acetyl-CoA-ACP transacylase, malonyl-CoA-ACP transacylase, and beta-ketoacyl-ACP synthase I were separated from one another and shown to have different molecular weights.
纤细裸藻是一种非常古老的真核生物，其叶绿体的获得和进化独立于高等植物。该生物体独特之处在于拥有两种从头脂肪酸合成酶，一种是细胞质中非常大的真正多酶复合体，另一种是由离散酶和酰基载体蛋白（ACP）组成的质体定位的II型脂肪酸合成酶。与大肠杆菌和植物相比，纤细裸藻II型脂肪酸合成酶中脂肪酸生物合成早期步骤的酶学有所不同。参与引发和延伸反应以形成新碳 - 碳键的纤细裸藻酶是乙酰辅酶A - ACP转酰基酶、丙二酰辅酶A - ACP转酰基酶和β - 酮酰基 - ACP合酶I。记录了抑制剂对这三种不同酶的影响。所有碳 - 碳键的形成都被浅蓝菌素抑制。尽管脂肪酸生物合成和任何一种分离出的酶都对二异丙基磷酰氟不敏感，但所研究的三种纤细裸藻酶对不同的巯基烷基化剂敏感。乙酰 - ACP支持脂肪酸生物合成的效果与等量的ACPSH和乙酰辅酶A相当。没有证据表明存在用于引发的β - 酮酰基 - ACP合酶III，如在高等植物和细菌的II型脂肪酸合成酶中所报道的那样。乙酰辅酶A - ACP转酰基酶和β - 酮酰基 - ACP合酶I在纤细裸藻II型脂肪酸合成酶中的作用似乎是独特的。乙酰辅酶A - ACP转酰基酶、丙二酰辅酶A - ACP转酰基酶和β - 酮酰基 - ACP合酶I彼此分离，并显示具有不同的分子量。
