Feb 25, 1976

Correlation of the kinetics of electron transfer activity of various eukaryotic cytochromes c with binding to mitochondrial cytochrome c oxidase

The Journal of Biological Chemistry
S Ferguson-MillerE Margoliash

Abstract

1. A detailed study of cytochrome c oxidase activity with Keilin-Hartree particles and purified beef heart enzyme, at low ionic strength and low cytochrome c concentrations, showed biphasic kinetics with apparent Km1 = 5 x 10(-8) M, and apparent Km2 = 0.35 to 1.0 x 10(-6) M. Direct binding studies with purified oxidase, phospholipid-containing as well as phospholiptaining aid-depleted, demonstrated two sites of interaction of cytochrome c with the enzyme, with KD1 less than or equal to 10(-7) M, and KD2 = 10(-6) M. 2. The maximal velocities as low ionic strength increased with pH and were highest above ph 7.5. 3. The presence and properties of the low apparent Km phase of the kinetics were strongly dependent on the nature and concentration of the anions in the medium. The multivalent anions, phosphate, ADP, and ATP, greatly decreased the proportion of this phase and similarly decreased the amount of high affinity cytochrome c-cytochrome oxidase complex formed. The order of effectiveness was ATP greater than ADP greater than P1 and since phosphate binds to cytochrome c more strongly than the nucleotides, it is concluded that the inhibition resulted from anion interaction with the oxidase. 4mat low concentrations bakers' yeast is...Continue Reading

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Mentioned in this Paper

Cytochrome C Oxidase
Cytochrome c Oxidase Subunit VIa
Beef heart preparation
Oxidase
Electron Transport
Succinates
Cytochrome c1 Activity
Myocardium
Mitochondrial Membranes
Phosphate Measurement

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