Component of the purine nucleotide cycle (PNC), which interconverts IMP and AMP to regulate the nucleotide levels in various tissues, and which contributes to glycolysis and ammoniagenesis. 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. Weakly inhibited by AMP non-competitively to all substrates. Inhibited by IMP non-competitively with respect to GTP. Inhibited by fructose 1,6-bisphosphate competitively with respect to IMP. Optimum pH is 6.6-6.9. Purine metabolism; AMP biosynthesis via de novo pathway; AMP from IMP: step 1/2. Homodimer. Partially associated with particulate fractions. High levels in muscle. Belongs to the adenylosuccinate synthetase family.