Gabler W L
Department of Biochemistry, School of Dentistry, Oregon Health Sciences University, Portland.
Res Commun Chem Pathol Pharmacol. 1990 Nov;70(2):213-26.
Recent studies have shown that, in cell free systems, Mg2+, but not Ca2+, is absolutely required for the generation of reducing equivalents by neutrophil NADPH oxidase. Apparently Mg2+ is required for binding of cytosolic protein(s) to the plasma membrane in forming a functional NADPH oxidase complex. Using intact neutrophils made permeable to Mg2+ and Ca2+ by A23187 it was found that Mg2+ was required for the generation of reducing equivalents by PMA stimulated cells while Ca2+ inhibited cytochrome c reduction. On the other hand, FMLP-induced neutrophils were unable to generate reducing equivalents unless both Ca2+ and Mg2+ were present in the media. Sequential addition of these cations indicated that Ca2+ was required for transduction of the FMLP-receptor generated signal to a point in the pathway where Mg2(+)-dependent synthesis of reducing equivalents occurred. This step, presumably, is the Mg2(+)-dependent completion of the NADPH oxidase complex. Finally, approximately 50% of the neutrophil's 2.19 fmoles (6.32 mM) of Mg2+ was found to be in a readily exchangeable pool and that pretreatment of neutrophils with either FMLP or PMA increased this pool by only 4-5%. This suggests there is an adequate pool of Mg2+ available to support completion of NADPH oxidase complex and that a stimulus-induced rise in free Mg2+ is not required to assist in the formation of the complex.
最近的研究表明，在无细胞体系中，中性粒细胞NADPH氧化酶产生还原当量绝对需要Mg2+，而不是Ca2+。显然，Mg2+是胞质蛋白与质膜结合以形成功能性NADPH氧化酶复合物所必需的。使用经A23187处理后对Mg2+和Ca2+通透的完整中性粒细胞，发现PMA刺激的细胞产生还原当量需要Mg2+，而Ca2+抑制细胞色素c的还原。另一方面，除非培养基中同时存在Ca2+和Mg2+，FMLP诱导的中性粒细胞无法产生还原当量。这些阳离子的顺序添加表明，Ca2+是将FMLP受体产生的信号转导至途径中发生Mg2+依赖性还原当量合成的位点所必需的。这一步骤大概是NADPH氧化酶复合物的Mg2+依赖性完成。最后，发现中性粒细胞2.19飞摩尔（6.32 mM）的Mg2+中约50%处于易于交换的池中，用FMLP或PMA预处理中性粒细胞只会使该池增加4-5%。这表明有足够的Mg2+池来支持NADPH氧化酶复合物的完成，并且不需要刺激诱导的游离Mg2+升高来协助复合物的形成。
