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

This study applies biophysical methods like light absorption spectrophotome try of cytochromes, determination of NAD(P)H-dependent superoxide anion (O- 2(-)) formation and localisation of hydroxyl radicals ((OH)-O-.) by 3-dimen sional (3D) confocal laser scanning microscopy to reveal in human cells put ative members of the oxygen sensing signal pathway leading to enhanced gene expression under hypoxia. A cell membrane localised non-mitochondrial cyto chrome b(558) seems to be involved as an oxygen sensor in the hepatoma cell line HepG2 in cooperation with the mitochondrial cytochrome b(563) probabl y probing additionally metabolic changes. (OH)-O-. the putative second mess enger of the oxygen sensing pathway generated by a Fenton reaction could be visualized in the perinuclear space of the three human cell lines used. Su bstances like cobalt or the iron chelator desferrioxamine, which have been applied in HepG2 cells to mimic hypoxia induced gene expression, interact o n various sides of the oxygen sensing pathway confirming the importance of b-type cytochromes and the Fenton reaction. (C) 1998 Elsevier Science B.V. All rights reserved.