Reaction: 2 GTP = diphosphate + P1,P4-bis(5'-guanosyl) tetraphosphate
Other names: diguanosine tetraphosphate synthetase; GTP-GTP guanylyltransferase; Gp4G synthetase; guanosine triphosphate-guanose triphosphate guanylyltransferase
Systematic name: GTP:GTP guanylyltransferase
Comments: Also acts, more slowly, on GDP to form P1,P3-bis(5'-guanosyl) triphosphate.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number: 54576-89-5
References:
1. Warner, A.H., Beers, P.C. and Huang, F.L. Biosynthesis of the diguanosine nucleotides. I. Purification and properties of an enzyme from yolk platelets of brine shrimp embryos. Can. J. Biochem. 52 (1974) 231-240. [PMID: 4208243]