Purification and properties of guanylate kinase from baker's yeast

Guanylate kinase (ATP:(d)GMP phosphotransferase, EC 2.7.4.8) was purified about 200-fold with 4% yield from baker's yeast. The enzyme preparation showed a single band on polyacrylamide gel electrophoresis and the molecular weight of the enzyme was calculated to be 25 000 by gel filtration. With ATP as a phosphate donor, the kinase used only GMP as a phosphate acceptor. Km values for ATP and GMP were 0.5 and 0.048 mM, respectively. The enzyme reacted optimally at pH 7.5. The enzyme was labile during storage at 4 degrees C and inactivation was prevented by 20% glycerol.