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 (By similarity). Plays a role in the regulation of adult life span. GTP + IMP + L-aspartate = GDP + 2 H(+) + N(6)-(1,2-dicarboxyethyl)-AMP + phosphate Binds 1 Mg(2+) ion per subunit. Purine metabolism; AMP biosynthesis via de novo pathway; AMP from IMP: step 1/2. Homodimer. Mutant flies show life span extension and increased activity. Heterozygous mutants show increased ratios of AMP:ATP (3 to 4-fold) and ADP:ATP (2-fold), also observed in response to caloric restriction, and associated with life span extension phenotypes in yeast and worms. Belongs to the adenylosuccinate synthetase family.