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It has been purified from many sources, such as Pseudomonas, [30] rat, [31] [32] [33] cow, [34] guinea pig [35] and human. [36] Recombinant human γ-butyrobetaine hydroxylase has also been produced by Escherichia coli [27] and baculoviruses [26] systems. Scheme describing the biosynthetic pathway of L-carnitine in humans.
Gamma-butyrobetaine dioxygenase (also known as BBOX, GBBH or γ-butyrobetaine hydroxylase) is an enzyme that in humans is encoded by the BBOX1 gene. [5] [6] Gamma-butyrobetaine dioxygenase catalyses the formation of L-carnitine from gamma-butyrobetaine, the last step in the L-carnitine biosynthesis pathway. [7]
The form present in the body is l-carnitine, which is also the form present in food. Food sources rich in l-carnitine are animal products, particularly beef and pork. [1] Red meats tend to have higher levels of l-carnitine. [1] [24] Adults eating diverse diets that contain animal products attain about 23–135 mg of carnitine per day.
Palmitoyl-CoA is an acyl-CoA thioester. It is an "activated" form of palmitic acid and can be transported into the mitochondrial matrix by the carnitine shuttle system (which transports fatty acyl-CoA molecules into the mitochondria), and once inside can participate in beta-oxidation.
Carnitine palmitoyltransferase I (CPT1) also known as carnitine acyltransferase I, CPTI, CAT1, CoA:carnitine acyl transferase (CCAT), or palmitoylCoA transferase I, is a mitochondrial enzyme responsible for the formation of acyl carnitines by catalyzing the transfer of the acyl group of a long-chain fatty acyl-CoA from coenzyme A to l-carnitine.
Acetyl-CoA carboxylase (ACC) is a biotin-dependent enzyme (EC 6.4.1.2) that catalyzes the irreversible carboxylation of acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT).
Carnitine O-acetyltransferase also called carnitine acetyltransferase (CRAT, or CAT) [5] (EC 2.3.1.7) is an enzyme that encoded by the CRAT gene that catalyzes the chemical reaction. acetyl-CoA + carnitine CoA + acetylcarnitine. where the acetyl group displaces the hydrogen atom in the central hydroxyl group of carnitine.
Malonyl-CoA is a highly regulated molecule in fatty acid synthesis; as such, it inhibits the rate-limiting step in beta-oxidation of fatty acids. Malonyl-CoA inhibits fatty acids from associating with carnitine by regulating the enzyme carnitine acyltransferase, thereby preventing them from entering the mitochondria, where fatty acid oxidation and degradation occur.