质膜上的活性氧制造者--NOX家族

NADPH氧化酶特异存在于吞噬细胞质膜，能生成用于清除病原微生物的活性氧（reactive oxygen species，ROS）。NOX是NADPH氧化酶催化亚基gp91^phox的同源物，存在于多种非吞噬细胞。目前发现的NOX有NOX1、NOX3、NOX4及NOX5，虽然它们有一定的组织特异性，但与NADPH氧化酶一样均有催化生成ROS的能力。与吞噬细胞中NADPH氧化酶所制造的ROS不同，NOX所产生的ROS并不主要起细胞防御功能，而是作为第二信使，参与细胞增殖、分化、凋亡的调节。此外，NOX对血管生成及骨吸收也有一定的影响，同时还可作为氧感受器调节促红细胞生成素（EPO）的产生。

NOX family: the ROS producer in plasma membrane

NADPH oxidase, specially located in plasma membrane of phagocytes, can generate reactive oxygen species (ROS) to participate in host defense by killing or damaging invading microbes. NOX are the homologs of gp91phox, the catalytic subunit of the NADPH oxidase, existing in various non-phagocytic cells. So far NOX1, NOX3, NOX4, NOX5 have been characterized. All of them possess the ability of ROS generation like NADPH oxidase, though their expression is tissue-specific. Unlike the NADPH oxidase-derived ROS that is responsible for cell defense, NOX- derived ROS functions as a second messenger molecule to participate in the modulation of cell proliferation, differentiation and apoptosis. In addition, NOX affects angiogenesis and bone resorption, and, as an oxygen sensor, regulates erythropoietin production.