GMP synthase (EC220.127.116.11, xanthosine-5'-phosphate—ammonia ligase, guanylate synthetase, XMP aminase, xanthosine 5'-monophosphate aminase) is an enzyme with system name xanthosine-5'-phosphate:ammonia ligase (AMP-forming). This enzyme catalyses the following chemical reaction
^Moyed, H.S. and Magasanik, B. (1957). "Enzymes essential for the biosynthesis of nucleic acid guanine; xanthosine 5′-phosphate aminase of Aerobacter aerogenes". J. Biol. Chem.226: 351–363. PMID13428768.