Function
Reactions
The entire process converts two amino groups, one from and one from::The reactions of the urea cycle 1 L- ornithine
2carbamoyl phosphate Carbamoyl phosphate is an anion of biochemical significance. In land-dwelling animals, it is an intermediary metabolite in nitrogen disposal through the urea cycle and the synthesis of pyrimidines. Its enzymatic counterpart, carbamoyl phosphate syn ...
3 L-citrulline The organic compound citrulline is an α-amino acid. Its name is derived from ''citrullus'', the Latin word for watermelon. Although named and described by gastroenterologists since the late 19th century, it was first isolated from watermelon in 1 ...
4argininosuccinate Argininosuccinic acid is a non-proteinogenic amino acid that is an important intermediate in the urea cycle. It is a basic amino acid. Reactions Some cells synthesize argininosuccinic acid from citrulline and aspartic acid and use it as a precur ...
5fumarate Fumaric acid is an organic compound with the formula HO2CCH=CHCO2H. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. The salts and esters are known as f ...
6 L-arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...
7urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...
L-Asp L-aspartate Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...
CPS-1carbamoyl phosphate synthetase I Carbamoyl phosphate synthetase I is a ligase enzyme located in the mitochondria involved in the production of urea. Carbamoyl phosphate synthetase I (CPS1 or CPSI) transfers an ammonia molecule to a molecule of bicarbonate that has been phospho ...
OTC Ornithine transcarbamoylase
ASSargininosuccinate synthetase Argininosuccinate synthase or synthetase (ASS; ) is an enzyme that catalyzes the synthesis of argininosuccinic acid, argininosuccinate from citrulline and aspartic acid, aspartate. In humans, argininosuccinate synthase is encoded by the ''ASS ...
ASL argininosuccinate lyase
ARG1arginase 1 Arginase (, ''arginine amidinase'', ''canavanase'', ''L-arginase'', ''arginine transamidinase'') is a manganese-containing enzyme. The reaction catalyzed by this enzyme is: : arginine + H2O → ornithine + urea It is the final enzyme of the ure ...
First reaction: entering the urea cycle
Before the urea cycle begins ammonia is converted to carbamoyl phosphate. The reaction is catalyzed bySteps of the urea cycle
#Carbamoyl phosphate is converted toOverall reaction equation
In the first reaction, + is equivalent to NH3 + CO2 + H2O. Thus, the overall equation of the urea cycle is: * NH3 + CO2 +Products of the urea cycle
As stated above many vertebrates use the urea cycle to create urea out of ammonium so that the ammonium does not damage the body. Though this is helpful, there are other effects of the urea cycle. For example: consumption of two ATP, production of urea, generation of H+, the combining of and to forms where it can be regenerated, and finally the consumption of .Regulation
''N''-Acetylglutamic acid
The synthesis of carbamoyl phosphate and the urea cycle are dependent on the presence of ''N''-acetylglutamic acid (NAcGlu), which allosterically activates CPS1. NAcGlu is an obligate activator of carbamoyl phosphate synthetase. Synthesis of NAcGlu by ''N''-acetylglutamate synthase (NAGS) is stimulated by both Arg, allosteric stimulator of NAGS, and Glu, a product in the transamination reactions and one of NAGS's substrates, both of which are elevated when freeSubstrate concentrations
The remaining enzymes of the cycle are controlled by the concentrations of their substrates. Thus, inherited deficiencies in cycle enzymes other thanLink with the citric acid cycle
The urea cycle and theUrea cycle disorders
Urea cycle disorders are rare and affect about one in 35,000 people in theIndividual disorders
* N-Acetylglutamate synthase (NAGS) deficiency * Carbamoyl phosphate synthetase (CPS) deficiency * Ornithine transcarbamoylase (OTC) deficiency * Citrullinemia type I (Deficiency of argininosuccinic acid synthase) * Argininosuccinic aciduria (Deficiency of argininosuccinic acid lyase) *Additional images
References
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