Purification and Properties of Guanylate Kinase from Escherichia coli

An enzyme, guanylate kinase, has been purified approximately 7000-fold from extracts of Escherichia coli. On the basis of its chromatographic profile, its sedimentation equilibrium pattern, its lack of tryptophan fluorescence, and its single zone in disc electrophoresis, it is a highly purified, if not homogeneous, protein species. It is specific for guanosine monophosphate or dGMP, and, in the presence of adenosine triphosphate, catalyzes the phosphorylation of these monophosphates to the corresponding diphosphates. The enzymatic activity is markedly stimulated by K+ and NH4+, but a kinetic analysis of the stimulation reveals that the two ions probably have different mechanisms of activation.