In enzymology, a guanylate kinase (EC 2.7.4.8) is an enzyme that catalyzes the chemical reaction:ATP + GMP ADP + GDP. Thus, the two substrates of this enzyme are ATP and GMP, whereas its two products are ADP and GDP. This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with a phosphate group as acceptor. This enzyme participates in purine metabolism.http://www.creative-enzymes.com/product/Native-Porcine-Guanylate-Kinase_1224.html