Tagatose-1,6-diphosphate activation of lactate dehydrogenase from Streptococcus cremoris

Tagatose-1,6-diphosphate was an effective substitute for fructose-1,6-diphosphate in the activation of lactate dehydrogenase (EC 1.1.1.27) from $\text{Streptococcus cremoris}$ AM2. The K_m for pyruvate, V_max and 0.5 values (activator concentration at half-maximal velocity) were similar with each activator. Of the other sugar phosphates and glycolytic intermediates tested only glucose-1,6-diphosphate activated the enzyme although the 0.5 value was 200 times that for the ketohexose diphosphates. Lactate dehydrogenases from several other organisms belonging to the Lactobacillaceae were equally stimulated by fructose-1,6-diphosphate and tagatose-1,6-diphosphate.