Argininosuccinate, biosynthesis

The enzymes that catalyze these steps are homologous to argininosuccinate synthetase and argininosuccinase, respectively. Thus, four of the five enzymes in the urea cycle were adapted from enzymes taking part in nucleotide biosynthesis. The remaining enzyme, arginase, appears to be an ancient enzyme found in all domains of life. 

Arginine, 2D biosynthesis, 435 catabolism, 431 134 chemical structure, 20 plasma concentration, 465 Argininosuccinate lyase, 439 Acgininosuccinate synthase, 439 Aromatic amino acids, chemical structure, 19 Arsenate, 840 Artenosclcrosis, 357 Arteriovenous differences, 19 199 Artery, physiology, 359 Ascoitale... 

R7. Ratner, S., Petrack, B., and Rochovansky, O., Biosynthesis of urea Part V. Isolation and properties of argininosuccinic acid. J. Biol. Chem. 204,95-113 (1953). 

L-argininosuccinate from citrulline and L-aspartate in the arginine biosynthesis pathway potential Cdc28p substrate... 

Adenylosuccinate formed by adenylosuccinate synthetase is cleaved by adenylosuccinate lyase to form AMP. The reaction steps are illustrated in Fig. 1. Included in the sequence is the additional reaction catalyzed by AMP deaminase. These three enzymes have been suggested to function in a cyclic process termed the purine nucleotide cycle 7,8). The two-step conversion of IMP to AMP is very similar to both the conversion of citrulline to arginine, which involves formation of argininosuccinate as an intermediate, and formation of 5-amino-imidazole 4-carboxamide ribonucleotide from 5-aminoimidazole 4-carboxylate ribonucleotide as part of IMP biosynthesis. Adenylosuccinate lyase is a dual function enzyme catalyzing the cleavage of both adenylosuccinate and 5-aminoimidazole 4-N-succinocarboxamide ribonucleotide. 

The enzymes discussed in the previous sections (carbamyl phosphate synthetase, ornithine transcarbamylase, argininosuccinate synthetase, cleavage enzyme, and arginase) constitute the known enzymic steps in the sequence of reactions leading to the biosynthesis of urea in ureotelic animals in accordance with the cycle originally proposed by Krebs and Hen-seleit (458). A summary scheme showing the steps in this cycle and the relationship of some of the intermediates to other systems is shown in Fig. 2. 

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