urea cycle
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Pathology
- carbamoyl phosphate synthase 1 deficiency
- ornithine transcarbamylase deficiency
- argininosuccinate synthetase deficiency (citrullinemia)
- argininosuccinate lyase deficiency (argininosuccinic aciduria)
- N-acetyl glutamate synthetase deficiency
- arginase deficiency
Biochemistry
- pathway confined to liver.
- in terrestial vertebrates, excess ammonia formed from the hepatic degradation of amino acids, is converted into urea, then excreted
- one of the nitrogen atoms of urea is transferred from aspartate, the other is derived from ammonia
- the carbon atom is derived from carbon dioxide
- aspartate is consumed in the urea cycle & fumarate is generated
* figure
- urea cycle 1
- enzyme: carbamoyl phosphate synthase NH3
- substrate: CO2 + NH3 + 2 ATP
- product: carbamoyl phosphate + 2 ADP + H2PO4-
- urea cycle 2
- enzyme: ornithine carbamoyltransferase
- substrate: ornithine + carbamoyl_phosphate
- product: citrulline + H2PO4-
- urea cycle 3
- enzyme: argininosuccinate synthetase
- substrate: citrulline + aspartate + ATP
- product: argininosuccinate + AMP + H2P2O7-2
- urea cycle 4
- enzyme: argininosuccinate lyase
- substrate: argininosuccinate
- product arginine + fumarate
- urea cycle 5