Thomas E L, Learn D B, Jefferson M M, Weatherred W
Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38101.
J Biol Chem. 1988 Feb 15;263(5):2178-86.
Incubation of stimulated neutrophils with sulfhydryl (RSH) compounds or ascorbic acid (ascorbate) results in rapid superoxide (O2-)-dependent oxidation of these reducing agents. Oxidation of RSH compounds to disulfides (RSSR) is faster than the rate of O2- production by the neutrophil NADPH-oxidase, whereas about one ascorbate is oxidized per O2-. Ascorbate is oxidized to dehydroascorbate, which is also oxidized but at a slower rate. Oxidation is accompanied by a large increase in oxygen (O2) uptake that is blocked by superoxide dismutase. Lactoferrin does not inhibit, indicating that ferric (Fe3+) ions are not required, and Fe3+-lactoferrin does not catalyze RSH or ascorbate oxidation. Two mechanisms contribute to oxidation: 1) O2- oxidizes ascorbate or reduced glutathione and is reduced to hydrogen peroxide (H2O2), which also oxidizes the reductants. O2- reacts directly with ascorbate, but reduced glutathione oxidation is mediated by the reaction of O2- with manganese (Mn2+). The H2O2-dependent portion of oxidation is mediated by myeloperoxidase-catalyzed oxidation of chloride to hypochlorous acid (HOCl) and oxidation of the reductants by HOCl. 2) O2- initiates Mn2+-dependent auto-oxidation reactions in which RSH compounds are oxidized and O2 is reduced. Part of this oxidation is due to the RSH-oxidase activity of myeloperoxidase. This activity is blocked by superoxide dismutase but does not require O2- production by the NADPH-oxidase, indicating that myeloperoxidase produces O2- when incubated with RSH compounds. It is proposed that an important role for O2- in the cytotoxic activities of phagocytic leukocytes is to participate in oxidation of reducing agents in phagolysosomes and the extracellular medium. Elimination of these protective agents allows H2O2 and products of peroxidase/H2O2/halide systems to exert cytotoxic effects.
用巯基（RSH）化合物或抗坏血酸（抗坏血酸盐）孵育受刺激的中性粒细胞，会导致这些还原剂迅速发生依赖超氧化物（O2-）的氧化。RSH化合物氧化为二硫化物（RSSR）的速度比中性粒细胞NADPH氧化酶产生O2-的速度快，而每产生一个O2-约有一个抗坏血酸盐被氧化。抗坏血酸盐被氧化为脱氢抗坏血酸盐，脱氢抗坏血酸盐也会被氧化，但速度较慢。氧化过程伴随着氧气（O2）摄取的大幅增加，而超氧化物歧化酶可阻断这种增加。乳铁蛋白不具有抑制作用，这表明不需要三价铁（Fe3+）离子，并且Fe3+ - 乳铁蛋白也不催化RSH或抗坏血酸盐的氧化。有两种机制促成氧化：1）O2-将抗坏血酸盐或还原型谷胱甘肽氧化，并被还原为过氧化氢（H2O2），H2O2也会氧化还原剂。O2-直接与抗坏血酸盐反应，但还原型谷胱甘肽的氧化是由O2-与锰（Mn2+）的反应介导的。氧化过程中依赖H2O2的部分是由髓过氧化物酶催化氯化物氧化为次氯酸（HOCl）以及HOCl氧化还原剂介导的。2）O2-引发依赖Mn2+的自动氧化反应，其中RSH化合物被氧化，O2被还原。这种氧化的一部分是由于髓过氧化物酶的RSH氧化酶活性。这种活性被超氧化物歧化酶阻断，但不需要NADPH氧化酶产生O2-，这表明髓过氧化物酶与RSH化合物孵育时会产生O2-。有人提出，O2-在吞噬性白细胞的细胞毒性活动中的一个重要作用是参与吞噬溶酶体和细胞外介质中还原剂的氧化。消除这些保护剂可使H2O2以及过氧化物酶/H2O2/卤化物系统的产物发挥细胞毒性作用。
