PathwayStep2501 PathwayStep2504 PathwayStep2502 PathwayStep2503 Carnitine synthesis Authored: 2003-04-29 00:00:00 Carnitine is synthesized in four steps from trimethyllysine (generated in turn by the S-adenosyl-methionine-mediated methylation of lysine residues in proteins, followed by protein hydrolysis). The enzymes that catalyze the first three steps of carnitine synthesis, converting trimethyllysine to gamma-butyrobetaine, are widely distributed in human tissues. The enzyme that catalyzes the last reaction, converting gamma-butyrobetaine to carnitine, is found only in liver and kidney cells, and at very low levels in brain tissues. Other tissues that require carnitine, such as muscle, are dependent on transport systems that mediate its export from the liver and uptake by other tissues (Kerner and Hoppel 1998). Edited: D'Eustachio, P, 0000-00-00 00:00:00 GENE ONTOLOGYGO:0045329 Pubmed9706223 Reactome Database ID Release 4371262 Reactome, http://www.reactome.org ReactomeREACT_2125 trimethyllysine + alpha-ketoglutarate + O2 => beta-hydroxy-trimethyllysine + succinate + CO2 gamma-butyrobetaine + alpha-ketoglutarate + O2 => carnitine + succinate + CO2 beta-hydroxy-trimethyllysine => gamma-butyrobetaine aldehyde + glycine gamma-butyrobetaine semialdehyde + NAD+ => gamma-butyrobetaine + NADH + H+