Cytochromes and oxygen radicals as putative members of the oxygen sensing pathway

This study applies biophysical methods like light absorption spectrophotometry of cytochromes, determination of NAD(P)H-dependent superoxide anion (O2-) formation and localisation of hydroxyl radicals (*OH) by 3-dimensional (3D) confocal laser scanning microscopy to reveal in human cells putative members of the oxygen sensing signal pathway leading to enhanced gene expression under hypoxia. A cell membrane localised non-mitochondrial cytochrome b558 seems to be involved as an oxygen sensor in the hepatoma cell line HepG2 in cooperation with the mitochondrial cytochrome b563 probably probing additionally metabolic changes. *OH the putative second messenger of the oxygen sensing pathway generated by a Fenton reaction could be visualized in the perinuclear space of the three human cell lines used. Substances like cobalt or the iron chelator desferrioxamine, which have been applied in HepG2 cells to mimic hypoxia induced gene expression, interact on various sides of the oxygen sensing pathway confirming the importance of b-type cytochromes and the Fenton reaction.