Duodenal cytochrome b: a novel ferrireductase in airway epithelial cells

ically active iron in the lung causes oxidative stress and promotes microbial growth that can be limited by intracellular sequestration of iron within ferritin. Because cellular iron uptake requires membrane ferrireductase activity that in the gut can be provided by duodenal cytochrome b (Dcytb), we sought Dcytb in the lung to test the hypothesis that it contributes to epithelial iron regulation by reducing Fe3 for cellular iron transport. Dcytb expression was found in respiratory epithelium in vitro and in vivo and was responsive to iron concentration. Iron transport was measured in human bronchial epi-thelial (HBE) cells using inductively coupled plasma atomic emission spectroscopy and was demonstrated to be partially inhibited in the presence of Dcytb-blocking antibody, suggesting that Dcytb reduces Fe3 for cellular iron transport. A definite source of reducing equiv-alents for Dcytb was sought but not identified. We found no evidence that ascorbate was involved but did demonstrate that O2 productio