Citric acid, also known as citrate or citronensaeure, belongs to the class of organic compounds known as tricarboxylic acids and derivatives. These are carboxylic acids containing exactly three carboxyl groups. Citric acid exists as a solid, soluble (in water), and a weakly acidic compound (based on its pKa). Citric acid has been found throughout all human tissues, and has also been detected in most biofluids, including urine, cerebrospinal fluid, saliva, and breast milk. Within the cell, citric acid is primarily located in the cytoplasm and mitochondria. Citric acid exists in all eukaryotes, ranging from yeast to humans. Citric acid participates in a number of enzymatic reactions. In particular, Citric acid can be biosynthesized from oxalacetic acid through the action of the enzyme citrate synthase, mitochondrial. In addition, Citric acid can be converted into cis-aconitic acid through the action of the enzyme aconitate hydratase, mitochondrial. In humans, citric acid is involved in the oncogenic action OF 2-hydroxyglutarate pathway, the citric Acid cycle pathway, the oncogenic action OF fumarate pathway, and the congenital lactic acidosis pathway. Citric acid is also involved in several metabolic disorders, some of which include the oncogenic action OF D-2-hydroxyglutarate in hydroxygluaricaciduria pathway, pyruvate dehydrogenase deficiency (e2), the oncogenic action OF L-2-hydroxyglutarate in hydroxygluaricaciduria pathway, and fumarase deficiency. Outside of the human body, citric acid can be found in a number of food items such as opium poppy, red raspberry, devilfish, and bamboo shoots. This makes citric acid a potential biomarker for the consumption of these food products. Citric acid has been found to be associated with several diseases known as rhabdomyolysis and deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures syndrome; citric acid has also been linked to several inborn metabolic disorders including maple syrup urine disease, primary hypomagnesemia, and tyrosinemia I.