No abstract

Ca2+-chelating agents, such as EDTA and ATP, are shown to bring about a rapid spectral response of the oxidized cytochrome c oxidase due to reversal of the Ca2+-induced red shift of the y-and a-absorption bands of the ferric enzyme. In addition, complexons are found to bring about Ca 2+-independent, slow irreversible spectral changes indicative of a conformational transition of cytochrome oxidase. 1 mol EDTA per mol enzyme is sufficient to produce the maximal effect even in the presence of excess Ca *+, indicating high specificity of interaction. It is suggested that the conformation of cytochrome c oxidase may be regulated by the tightly bound 'non-redox' metal ions (Mg, Zn, Cu,) known to be present in the enzyme. These ions might be involved in specific binding of physiological effecters with chelating properties, such as ATP.

Electron transfer through the ubiquinol:cytochrome c 1‐segment of liver mitochondria isolated from hibernating ground squirrels Citellus undulatus is repressed by 70–80% as compared to mitochondria from the active animals. The inhibition site is likely to be localized between ubiquinone and the cytochrome bc 1, complex. Partial release of the inhibition can be observed upon swelling of the isolated mitochondria in a hypoosmotie medium, the effect being prevented by phospholipase A2 inhibitors. Possible role of phospholipase A2 in regulation of ubiquinol oxidation by complex bc 1, is discussed.