Phosphoglycerate kinase from yeast synthesizes guanosine 5'-tetraphosphate

Yeast phosphoglycerate kinase (PGK; EC 2.7.2.3) synthesizes adenosine 5'-tetraphosphate (ppppA) from ATP and 1,3-bisphosphoglycerate. Using an HPLC assay, we have shown the synthesis of guanosine 5'-tetraphosphate (ppppG; 0.17 nmol.min-1.PGK unit-1) characterized by its u.v. spectrum, HPLC behavior, and enzymatic digestions. That the synthesis of ppppG is catalyzed by PGK itself and not by a contaminant was shown because it depended on 3-phosphoglycerate (as a source of 1,3-bisphosphoglycerate), coeluted with PGK activity upon gel filtration, and the thermal inactivation of the PGK and the ppppG synthetic activity were parallel.