Adenylosuccinate synthetase and method for producing purine nucleotides using the same

An adenylosuccinate synthetase variant having at least 90% sequence identity to the amino acid sequence of SEQ ID NO:2 and having adenylosuccinate synthetase activity, wherein the amino acid corresponding to position 85 of the amino acid sequence of SEQ ID NO:

• 2 is substituted with a different amino acid, wherein the different amino acid is selected from the group consisting of serine, alanine, valine, leucine, methionine, isoleucine, threonine, asparagine, glutamine, cysteine, tyrosine, lysine, aspartic acid, and glutamic acid, and wherein said adenylosuccinate synthetase variant has increased purine production relative to a wild type adenylosuccinate synthetase.