Succinic acid
Succinic acid (səkˈsɪnᵻk) is a dicarboxylic acid with the chemical formula (CH2)2(CO2H)2. In living organisms, succinic acid takes the form of an anion, succinate, which has multiple biological roles as a metabolic intermediate being converted into fumarate by the enzyme succinate dehydrogenase in complex 2 of the electron transport chain which is involved in making ATP, and as a signaling molecule reflecting the cellular metabolic state. Succinate is generated in mitochondria via the tricarboxylic acid cycle (TCA). Succinate can exit the mitochondrial matrix and function in the cytoplasm as well as the extracellular space, changing gene expression patterns, modulating epigenetic landscape or demonstrating hormone-like signaling. As such, succinate links cellular metabolism, especially ATP formation, to the regulation of cellular function. Dysregulation of succinate synthesis, and therefore ATP synthesis, happens in some genetic mitochondrial diseases, such as Leigh syndrome, and Melas syndrome, and degradation can lead to pathological conditions, such as malignant transformation, inflammation and tissue injury. Succinic acid is marketed as food additive E363. The name derives from Latin succinum, meaning amber. Succinic acid is a white, odorless solid with a highly acidic taste. In an aqueous solution, succinic acid readily ionizes to form its conjugate base, succinate (ˈsʌksᵻneɪt). As a diprotic acid, succinic acid undergoes two successive deprotonation reactions: (CH2)2(CO2H)2 → (CH2)2(CO2H)(CO2)− + H+ (CH2)2(CO2H)(CO2)− → (CH2)2(CO2)22− + H+ The pKa of these processes are 4.3 and 5.6, respectively. Both anions are colorless and can be isolated as the salts, e.g., Na(CH2)2(CO2H)(CO2) and Na2(CH2)2(CO2)2. In living organisms, primarily succinate, not succinic acid, is found. As a radical group it is called a succinyl (ˈsʌksᵻnəl) group. Like most simple mono- and dicarboxylic acids, it is not harmful but can be an irritant to skin and eyes. Historically, succinic acid was obtained from amber by distillation and has thus been known as spirit of amber.
