Sherman D R, Guinn B, Perdok M M, Goldberg D E
Department of Medicine, Washington University School of Medicine, St. Louis, MO.
Science. 1992 Dec 18;258(5090):1930-2. doi: 10.1126/science.1470914.
The parasitic nematode Ascaris infests a billion people worldwide. Much of its proliferative success is due to prodigious egg production, up to 10(6) sterol-replete eggs per day. Sterol synthesis requires molecular oxygen for squalene epoxidation, yet oxygen is scarce in the intestinal folds the worms inhabit. Ascaris has an oxygen-avid hemoglobin in the perienteric fluid that bathes its reproductive organs. Purified hemoglobin contained tightly bound squalene and functioned as an NADPH-dependent, ferrihemoprotein reductase. All components of the squalene epoxidation reaction--squalene, oxygen, NADPH, and NADPH-dependent reductase--are assembled on the hemoglobin. This molecule may thus function in sterol biosynthesis.
寄生线虫蛔虫在全球感染了十亿人。其繁殖成功很大程度上归因于大量产卵，每天可产出多达10⁶个富含甾醇的卵。甾醇合成需要分子氧进行角鲨烯环氧化，但蛔虫栖息的肠皱襞中氧气稀缺。蛔虫在包围其生殖器官的肠周液中有一种对氧有高度亲和力的血红蛋白。纯化的血红蛋白含有紧密结合的角鲨烯，并作为一种依赖NADPH的高铁血红蛋白还原酶发挥作用。角鲨烯环氧化反应的所有成分——角鲨烯、氧气、NADPH和依赖NADPH的还原酶——都聚集在血红蛋白上。因此，这种分子可能在甾醇生物合成中发挥作用。
