In vitro activation of phosphoglucomutase by fructose 2,6-bisphosphate.

The hexose bisphosphate activation of phosphoglucomutase was investigated with both plant (pea and mung bean) and animal (rabbit muscle) sources of the enzyme. Plant phosphoglucomutase was purified about 50-fold from seeds, and to a lesser extent, from seedlings of Pisum sativum L. cv Grenadier and seedlings of Phaseolus aureus. It was found that the plant enzyme was isolated in a mostly dephosphorylated form while commercial rabbit muscle phosphoglucomutase was predominantly in the phosphorylated form. Activation studies were done using the dephosphorylated enzymes. The range of activation constant (K(a)) values were obtained for each bisphosphate were: for glucose 1-6-P(2), 0.5 to 1.8; fructose 2,6-P(2), 6 to 11.7; and fructose 1,6-P(2), 7 micromolar, respectively. Fructose 2,6-P(2) is known to occur in both plant and animal tissues at changing levels encompassing the K(a) values found in this study; hence, these results implicate fructose 2,6-P(2) as a natural activator of phosphoglucomutase, particularly in plants. Also, glucose 1,6-P(2) has not been found in plants, and the method for measuring glucose 1,6-P(2) by monitoring the activation of phosphoglucomutase is not specific.