Plays an important role in the de novo pathway and in the salvage pathway of purine nucleotide biosynthesis. Catalyzes the first committed step in the biosynthesis of AMP from IMP. GTP + IMP + L-aspartate = GDP + 2 H(+) + N(6)-(1,2-dicarboxyethyl)-AMP + phosphate Binds 1 Mg(2+) ion per subunit. Inhibited by GMP. Inhibited by chloride. Inhibited in a highly specific manner by the binding of a 44-base DNA oligonucleotide carrying the ARS core consensus sequence. Optimum pH is 8.0. Optimum temperature is 35 degrees Celsius. Purine metabolism; AMP biosynthesis via de novo pathway; AMP from IMP: step 1/2. Homodimer. Present with 56800 molecules/cell in log phase SD medium. Belongs to the adenylosuccinate synthetase family.