The Production of Superoxide Radicals in Biological Systems

An EPR signal, characteristic for the superoxide radical, was observed by the rapid-freezing technique in the oxidation at pH 10 of xanthine by dioxygen catalysed by xanthine oxidase (EC 1,2.3.2) The enzymatic reduction of dioxygen by aldehyde oxidase (EC 1.2.3.1) produces also the superoxide radical. 

The plasma-membrane bound superoxide-generating flavoprotein (superoxide synthetase) of human polymorphonuclear neutrophils (PMN) has been solubilized by Triton X-100and deoxycholate and purified. The enzyme catalyses the reaction  

The value for NADPH is of the order of 35 pM against 900 pM for NADH. NAD(P)H seems to react on the cytosolic side of the membrane, while the superoxide anion is generated at the outer side 

Following a stimulation by the yeast cell wall extract zymosan, phagocytosing human leukocytes show an enhanced oxygen consumption, the cyanide-insensitive respiratory burst , after a lag period of 30-40 s. The production of superoxide anions, measured by the reduction of Fe(ni)-cytochrome c, followed the same 

A similar enzymatic activity was found in stimulated pulmonar alveolar macrophages from humans guinea pigs and rats and in retinal pigment epithelial cells from chick embryos 

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