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[摘要]：The oxidative pentose phosphate cycle (OPPC) is necessary to maintain cellular reducing capacity during periods of increased oxidative stress. Metabolic flux through the OPPC increases stoichiometrically in response to a broad range of chemical oxidants, including those that generate reactive oxygen species (ROS). Here we show that OPPC sensitivity is sufficient to detect low levels of ROS produced metabolically as a function of the percentage of O-2. We observe a significant decrease in OPPC activity in cells incubated under severe and moderate hypoxia (ranging from <0.01 to 4% O-2), whereas hyperoxia (95% O-2) results in a significant increase in OPPC activity. These data indicate that metabolic ROS production is directly dependent on oxygen concentration. Moreover, we have found no evidence to suggest that ROS, produced by mitochondria, are needed to stabilize hypoxia-inducible factor 1 alpha(HIF-1 alpha) under moderate hypoxia. Myxothiazol, an inhibitor of mitochondrial electron transfer, did not prevent HIF-1 alpha stabilization under moderate hypoxia. Moreover, the levels of HIF-1 alpha that we observed after exposure to moderate hypoxia were comparable between rho(0) cells, which lack functional mitochondria, and the wild-type cells. Finally, we find no evidence for stabilization of HIF-1 alpha in response to the non-toxic levels of H2O2 generated by the enzyme glucose oxidase. Therefore, we conclude that the oxygen dependence of the prolyl hydroxylase reaction is sufficient to mediate HIF-1 alpha stability under moderate as well as severe hypoxia. |
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