Mitochondrial carbonic anhydrase that catalyzes the reversible conversion of carbon dioxide to bicarbonate/HCO3 (PubMed:24530203, PubMed:8356065). Mitochondria are impermeable to HCO3, and thus this intramitochondrial carbonic anhydrase is pivotal in providing HCO3 for multiple mitochondrial enzymes that catalyze the formation of essential metabolites of intermediary metabolism in the urea and Krebs cycles (PubMed:24530203)

Mitochondrion

Hyperammonemia due to carbonic anhydrase VA deficiency

An autosomal recessive inborn error of metabolism, clinically characterized by infantile hyperammonemic encephalopathy. Metabolic abnormalities include hypoglycemia, hyperlactatemia, metabolic acidosis and respiratory alkalosis.

Catalyzes the reversible cleavage of L-argininosuccinate to fumarate and L-arginine, an intermediate step reaction in the urea cycle mostly providing for hepatic nitrogen detoxification into excretable urea as well as de novo L-arginine synthesis in nonhepatic tissues (PubMed:11747432, PubMed:11747433, PubMed:22081021, PubMed:2263616, PubMed:9045711). Essential regulator of intracellular and extracellular L-arginine pools. As part of citrulline-nitric oxide cycle, forms tissue-specific multiprot

Argininosuccinic aciduria

An autosomal recessive disorder of the urea cycle. The disease is characterized by mental and physical retardation, liver enlargement, skin lesions, dry and brittle hair showing trichorrhexis nodosa microscopically and fluorescing red, convulsions, and episodic unconsciousness.

Biotin-attachment subunit of the 3-methylcrotonyl-CoA carboxylase, an enzyme that catalyzes the conversion of 3-methylcrotonyl-CoA to 3-methylglutaconyl-CoA, a critical step for leucine and isovaleric acid catabolism

Mitochondrion matrix

3-methylcrotonoyl-CoA carboxylase 1 deficiency

An autosomal recessive disorder of leucine catabolism. The phenotype is variable, ranging from neonatal onset with severe neurological involvement to asymptomatic adults. There is a characteristic organic aciduria with massive excretion of 3-hydroxyisovaleric acid and 3-methylcrotonylglycine, usually in combination with a severe secondary carnitine deficiency.

Key element of the urea cycle converting L-arginine to urea and L-ornithine, which is further metabolized into metabolites proline and polyamides that drive collagen synthesis and bioenergetic pathways critical for cell proliferation, respectively; the urea cycle takes place primarily in the liver and, to a lesser extent, in the kidneys Functions in L-arginine homeostasis in nonhepatic tissues characterized by the competition between nitric oxide synthase (NOS) and arginase for the available int

CytoplasmCytoplasmic granule

Argininemia

A rare autosomal recessive disorder of the urea cycle. Arginine is elevated in the blood and cerebrospinal fluid, and periodic hyperammonemia occurs. Clinical manifestations include developmental delay, seizures, intellectual disability, hypotonia, ataxia and progressive spastic quadriplegia.

One of the enzymes of the urea cycle, the metabolic pathway transforming neurotoxic amonia produced by protein catabolism into inocuous urea in the liver of ureotelic animals. Catalyzes the formation of arginosuccinate from aspartate, citrulline and ATP and together with ASL it is responsible for the biosynthesis of arginine in most body tissues

Cytoplasm, cytosol

Citrullinemia 1

The classic form of citrullinemia, an autosomal recessive disease characterized primarily by elevated serum and urine citrulline levels. Ammonia intoxication is another manifestation. It is a disorder of the urea cycle, usually manifesting in the first few days of life. Affected infants appear normal at birth, but as ammonia builds up in the body they present symptoms such as lethargy, poor feeding, vomiting, seizures and loss of consciousness. Less commonly, a milder form can develop later in childhood or adulthood.

Mitochondrial electrogenic aspartate/glutamate antiporter that favors efflux of aspartate and entry of glutamate and proton within the mitochondria as part of the malate-aspartate shuttle (PubMed:11566871, PubMed:38937634, PubMed:38945283, PubMed:39419476). Substrate exchange across the membrane occurs consecutively with one substrate being transported first, then dissociating from the substrate binding site before the second substrate binds for transport in the opposite direction (PubMed:389376

Mitochondrion inner membrane

Citrin deficiency, adolescent or adult onset

An autosomal recessive metabolic disorder characterized by elevated serum and urine citrulline levels, ammonia intoxication, and neuropsychiatric symptoms including abnormal behaviors, loss of memory, seizures and coma. Death can result from brain edema.

Involved in the urea cycle of ureotelic animals where the enzyme plays an important role in removing excess ammonia from the cell

MitochondrionNucleus, nucleolusCell membrane

Carbamoyl phosphate synthetase 1 deficiency

An autosomal recessive disorder of the urea cycle causing hyperammonemia. It can present as a devastating metabolic disease dominated by severe hyperammonemia in neonates or as a more insidious late-onset condition, generally manifesting as life-threatening hyperammonemic crises under catabolic situations. Clinical features include protein intolerance, intermittent ataxia, seizures, lethargy, developmental delay and intellectual disability.

Plays a role in the regulation of ureagenesis by producing the essential cofactor N-acetylglutamate (NAG), thus modulating carbamoylphosphate synthase I (CPS1) activity

Mitochondrion matrix

N-acetylglutamate synthase deficiency

Rare autosomal recessively inherited metabolic disorder leading to severe neonatal or late-onset hyperammonemia without increased excretion of orotic acid. Clinical symptoms are somnolence, tachypnea, feeding difficulties, a severe neurologic presentation characterized by uncontrollable movements, developmental delay, visual impairment, failure to thrive and hyperammonemia precipitated by the introduction of high-protein diet or febrile illness.

Mitochondrial glutamate dehydrogenase that catalyzes the conversion of L-glutamate into alpha-ketoglutarate. Plays a key role in glutamine anaplerosis by producing alpha-ketoglutarate, an important intermediate in the tricarboxylic acid cycle (PubMed:11032875, PubMed:11254391, PubMed:16023112, PubMed:16959573). Plays a role in insulin homeostasis (PubMed:11297618, PubMed:9571255). May be involved in learning and memory reactions by increasing the turnover of the excitatory neurotransmitter gluta

MitochondrionEndoplasmic reticulum

Hyperinsulinemic hypoglycemia, familial, 6

A form of hyperinsulinemic hypoglycemia, a clinically and genetically heterogeneous disorder characterized by inappropriate insulin secretion from the pancreatic beta-cells in the presence of low blood glucose levels. HHF6 is an autosomal dominant form characterized by hypoglycemia due to congenital hyperinsulinism combined with persistent hyperammonemia. Clinical features include loss of consciousness due to hypoglycemia, hypoglycemic seizures, and mental retardation.

Catalyzes the second step of the urea cycle, the condensation of carbamoyl phosphate with L-ornithine to form L-citrulline (PubMed:2556444, PubMed:6372096, PubMed:8112735). The urea cycle ensures the detoxification of ammonia by converting it to urea for excretion (PubMed:2556444)

Mitochondrion matrix

Ornithine carbamoyltransferase deficiency

An X-linked disorder of the urea cycle which causes a form of hyperammonemia. Mutations with no residual enzyme activity are always expressed in hemizygote males by a very severe neonatal hyperammonemic coma that generally proves to be fatal. Heterozygous females are either asymptomatic or express orotic aciduria spontaneously or after protein intake. The disorder is treatable with supplemental dietary arginine and low protein diet. The arbitrary classification of patients into the 'neonatal' group (clinical hyperammonemia in the first few days of life) and 'late' onset (clinical presentation after the neonatal period) has been used to differentiate severe from mild forms.

Mitochondrial ornithine-citrulline antiporter (Probable) (PubMed:12807890, PubMed:22262851). Catalyzes the exchange between cytosolic ornithine and mitochondrial citrulline plus an H(+), the proton compensates the positive charge of ornithine thus leading to an electroneutral transport. Plays a crucial role in the urea cycle, by connecting the cytosolic and the intramitochondrial reactions of the urea cycle (Probable) (PubMed:12807890, PubMed:22262851). Lysine and arginine are also transported b

Mitochondrion inner membraneMitochondrion membrane

Hyperornithinemia-hyperammonemia-homocitrullinuria syndrome

An autosomal recessive disorder of the urea cycle characterized by onset in early life. The acute phase of the disease is characterized by vomiting, ataxia, lethargy, confusion, and coma. Chronic clinical manifestations include hypotonia, developmental delay, progressive encephalopathy with mental regression, and spastic paraparesis with pyramidal signs.