Early reduction of cytochrome c in hypoxia

Shifts of the steady state of cytochromes a, a3 and c at high pO2 values are cited as evidence of the low O2 affinity of cytochrome oxidase in vivo [(1971) Brain Res. 108, 143-154; (1985) Adv. Exp. Med. Biol. 191, 833-842; (1987) in: Int. Soc. Oxygen Transp. Tissue, Sapporo, p. 84]. Highly aerobic, small diploid yeast cells show less than 0.44% change of steady state in the interval prior to an abrupt reduction of cytochrome c. Thus, 'pre-reduction' seems falsified as a physiological response of metabolizing yeast cells that are free of hemoglobin, do not aggregate and maintain a steady state. Pre-reduction may be due to spectroscopic interference, for example hemoglobin deoxygenation, to oxygen gradients in aggregated cells and tissues or to non-steady states of substrate and metabolic controls, as contrasted to an altered cytochrome oxidase oxygen affinity in vivo.