The interaction of ferrocytochrome c with long-chain fatty acids and their CoA and carnitine esters

Non-covalent modification of cytochrome c may have implications for electron transport and energy metabolism. We examined the interaction of various fatty acids (FAs), their coenzyme A and carnitine esters, and fatty alcohols with horse heart ferrocytochrome c. A comparison of FAs indicated a minimum chain length of 14 carbons was required for significant effect on the ferroheme chromophore and major changes in electronic spectra. Coenzyme A and carnitine esters interacted less strongly than FAs whereas long-chain alcohols did not interact with the protein. We found a single, saturable FA binding site with Kd (oleate) of 23.1 µM (by stopped-flow kinetics), 30 µM (by radiochemical binding assay), and 29 µM (by spectrophotometric assay). The binding stoichiometry was 1:1. We present evidence from electronic spectra, and proton NMR (nuclear magnetic resonance) that the S–Fe coordination (methionine 80) was disrupted by ligand binding. From molecular modeling we identify a putative binding channel flanked by lysines 72 and 73.