Urea Cycle PDF

254 19. Amino Acids: Disposal of Nitrogen Tissues other than liver use enzymes 8 of this pathway to make arginine. –...

254 19. Amino Acids: Disposal of Nitrogen Tissues other than liver use enzymes 8 of this pathway to make arginine. – H COO CYTOSOL C NH 2 C C NH2+ H2N – OOC H NH H2O C O H2N Malate Fumarate CH2 Urea Ornithine is regenerated CH2 6 and transported into the CH2 mitochondrion. HCNH3+ COO – Arginase MITOCHONDRIAL Arginino- MATRIX succinate L-Arginine NH3+ NH3 + NH3+ COO – lyase CH2 CH2 C N CH CH2 CH2 NH CH2 CH2 CH2 CH2 COO– HCNH3+ HCNH3+ CH2 COO – COO – CH2 L-Ornithine L-Ornithine HCNH3+ – COO NH2 Argininosuccinate CO Ornithine trans- O carbamoylase 4 Citrulline is transported out of the mitochondrion. – O P O – O Carbamoyl phosphate NH 2 NH2 C O C O Argininosuccinate synthetase NH NH Pi AMP + CH2 CH2 PPi CH2 CH2 CH2 CH2 3H+ ATP + HCNH3+ HCNH3+ 2ADP COO– COO– + – Pi COO L-Citrulline L-Citrulline +H N CH Carbamoyl 3 phosphate synthetase I CH2 – COO The amino group of aspartate CO 2 5 provides one of the L-Aspartate + nitrogen atoms of urea. NH 3 Carbon dioxide provides 1 the carbon atom of urea. + 2A ATP te Oxaloacetate Free ammonia provides 2 one of the nitrogen Glutamate α-Ketoglutarate atoms of urea. The enzyme has an absolute 3 requirement for N-acetyl- Fumarate is hydrated to 7 malate, which is oxidized glutamate, which acts as an allosteric activator. to oxaloacetate, which is transaminated to aspartate. Figure 19.14 Reactions of the urea cycle.