In biochemistry and metabolism, beta-oxidation is the catabolic process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

in eukaryotes to generate

acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for ...

, which enters the citric acid cycle, and NADH and FADH₂, which are co-enzymes used in the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

. It is named as such because the

beta carbon In the nomenclature of organic chemistry, a locant is a term to indicate the position of a functional group or substituent within a molecule. Numeric locants The International Union of Pure and Applied Chemistry (IUPAC) recommends the use of ...

of the fatty acid undergoes oxidation to a carbonyl group. Beta-oxidation is primarily facilitated by the

mitochondrial trifunctional protein Mitochondrial trifunctional protein (MTP) is a protein attached to the inner mitochondrial membrane which catalyzes three out of the four steps in beta oxidation. MTP is a hetero-octamer composed of four alpha and four beta subunits: * HADHA * HA ...

, an enzyme complex associated with the inner mitochondrial membrane, although very long chain fatty acids are oxidized in

peroxisome A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen pero ...

s. The overall reaction for one cycle of beta oxidation is: :C_''n''-acyl-CoA + FAD + + + CoA → C_''n''-2-acyl-CoA + + NADH + + acetyl-CoA

Activation and membrane transport

Free fatty acids cannot penetrate any biological membrane due to their negative charge. Free fatty acids must cross the cell membrane through specific transport proteins, such as the SLC27 family fatty acid transport protein. Once in the cytosol, the following processes bring fatty acids into the mitochondrial matrix so that beta-oxidation can take place. # Long-chain-fatty-acid—CoA ligase catalyzes the reaction between a fatty acid with

ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals, men's professional tennis governing body * American Technical Publishers, employee-owned publishing company * ', a Danish pension * Armenia Tree Project, non ...

to give a fatty acyl adenylate, plus inorganic pyrophosphate, which then reacts with free

coenzyme A Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All genomes sequenced to date encode enzymes that use coenzyme A as a subs ...

to give a fatty acyl-CoA ester and AMP. #If the fatty acyl-CoA has a long chain, then the

carnitine shuttle Carnitine is a quaternary ammonium compound involved in metabolism in most mammals, plants, and some bacteria. In support of energy metabolism, carnitine transports long-chain fatty acids into mitochondria to be oxidized for energy production, an ...

must be utilized: ##Acyl-CoA is transferred to the hydroxyl group of carnitine by carnitine palmitoyltransferase I, located on the cytosolic faces of the

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