Fatty acid oxidation is a multi-step process by which fatty acids are broken down in β-oxidation to generate acetyl-CoA, NADH and FADH2 for further electron transfer to CoQ. Whereas NADH is the substrate of CI, FADH2 is the substrate of electron-transferring flavoprotein complex (CETF) which is localized on the matrix face of the mtIM, and supplies electrons from FADH2 to CoQ. Before the ß-oxidation in the mitochondrial matrix, fatty acids (short-chain with 1-6, medium-chain with 7–12, long-chain with >12 carbon atoms) are activated by fatty acyl-CoA synthases (thiokinases) in the cytosol. For the mitochondrial transport of long-chain fatty acids the mtOM-enzyme carnitine palmitoyltransferase I (CPT-1; considered as a rate-limiting step in FAO) is required which generates an acyl-carnitine intermediate from acyl-CoA and carnitine. In the next step, an integral mtIM protein carnitine-acylcarnitine translocase (CACT) catalyzes the entrance of acyl-carnitines into the mitochondrial matrix in exchange for free carnitines. In the inner side of the mtIM, another enzyme carnitine palmitoyltransferase 2 (CPT-2) converts the acyl-carnitines to carnitine and acyl-CoAs, which undergo ß-oxidation in the mitochondrial matrix. Short- and medium-chain fatty acids do not require the carnitine shuttle for mitochondrial transport. Octanoate, but not palmitate, (eight- and 16-carbon saturated fatty acids) may pass the mt-membranes, but both are frequently supplied to mt-preparations in the activated form of octanoylcarnitine or palmitoylcarnitine.
Reference: Gnaiger 2020 BEC MitoPathways
MitoPedia O2k and high-resolution respirometry: O2k-Open Support
FAO and HRR
- FAO cannot proceed without a substrate combination of fatty acids & malate, and inhibition of CI blocks FAO completely. Fatty acids are split stepwise into two carbon fragments forming acetyl-CoA, which enters the TCA cycle by condensation with oxaloacetate (CS reaction). Therefore, FAO implies simultaneous electron transfer into the Q-junction through CETF and CI.
SUITbrowser question: Fatty acid oxidation
- Lemieux H, Semsroth S, Antretter H, Höfer D, Gnaiger E (2011) Mitochondrial respiratory control and early defects of oxidative phosphorylation in the failing human heart. Int J Biochem Cell Biol 43:1729–38. »Bioblast Access«
- Pesta D, Hoppel F, Macek C, Messner H, Faulhaber M, Kobel C, Parson W, Burtscher M, Schocke M, Gnaiger E (2011) Similar qualitative and quantitative changes of mitochondrial respiration following strength and endurance training in normoxia and hypoxia in sedentary humans. Am J Physiol Regul Integr Comp Physiol 301:R1078–87. »Open Access«
- Pesta D, Gnaiger E (2012) High-resolution respirometry. OXPHOS protocols for human cells and permeabilized fibres from small biopsies of human muscle. Methods Mol Biol 810:25-58. »Bioblast Access«
- Oliveira AF, Cunha DA, Ladriere L, Igoillo-Esteve M, Bugliani M, Marchetti P, Cnop M (2015) In vitro use of free fatty acids bound to albumin: A comparison of protocols. Biotechniques 58:228-33. »Open Access«
- » O2k-Network discussion forum: fatty acids used in permeabilized fibre assays
- » F-pathway control state
MitoPedia methods: Respirometry
MitoPedia topics: Substrate and metabolite