Ligation, inhibition, and activation of cytochrome c oxidase by fatty acids

Free fatty acids bind to beef heart cytochrome c oxidase and induce spectral shifts similar to those obtained with high spin ligands. Oleic (18:1(n-9)) and linoleic (18:2(n-6)) acids induce substantial blue shifts of the Soret peak of oxidized enzyme. Small saturated fatty acids (<15 carbon atoms) shift the Soret peak to the red, and longer chain acids induce smaller blue shifts. Formate-induced spectral shifts are modified by short chain fatty acids but are unaffected by longer chain fatty acids for which effects are additive with those of formate. Inhibition by formate is partially relieved by all fatty acids tested. Palmitic and linoleic acids increase turnover at low cytochrome c levels and decrease the K_m for cytochrome c at high cytochrome c levels. Oleic acid protects the enzyme against acid denaturation during turnover. Bovine serum albumin produces a red shift in the oxidase Soret peak and inhibits turnover of the isolated enzyme. Oleic acid and serum albumin modify the electron paramagnetic resonance spectrum of oxidized oxidase, oleic acid shifting the g = 3 (cytochrome a) peak towards low field and albumin towards higher field strengths. The oxidase may possess at least two fatty acid binding sites at one of which cytochrome c binding is modulated and at another spectral changes may be induced. One site is close enough to the binuclear centre to interact allosterically with ligand binding at that centre.