Free fatty acids bind to beef heart cytochrome c oxidase and induce sp
ectral shifts similar to those obtained with high spin ligands. Oleic
(18:1(n-9)) and linoleic (18:2(n-6)) acids induce substantial blue shi
fts of the Soret peak of oxidized enzyme. Small saturated fatty acids
(<15 carbon atoms) shift the Soret peak to the red, and longer chain a
cids induce smaller blue shifts. Formate-induced spectral shifts are m
odified by short chain fatty acids but are unaffected by longer chain
fatty acids for which effects are additive with those of formate. Inhi
bition by formate is partially relieved by all fatty acids tested. Pal
mitic and linoleic acids increase turnover at low cytochrome c levels
and decrease the K-m for cytochrome c at high cytochrome c levels. Ole
ic acid protects the enzyme against acid denaturation during turnover.
Bovine serum albumin produces a red shift in the oxidase Soret peak a
nd inhibits turnover of the isolated enzyme. Oleic acid and serum albu
min modify the electron paramagnetic resonance spectrum of oxidized ox
idase, oleic acid shifting the g = 3 (cytochrome a) peak towards low f
ield and albumin towards higher field strengths. The oxidase may posse
ss at least two fatty acid binding sites at one of which cytochrome c
binding is modulated and at another spectral changes may be induced. O
ne site is close enough to the binuclear centre to interact allosteric
ally with ligand binding at that centre.