In Vitro Activation of Phosphoglucomutase by Fructose 2,6-Bisphosphate

Abstract

The hexose bisphosphate activation of phosphoglucomutase was investipted 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.) values were obtained for each bisphosphate were: for glucose 1-6-P2, 0.5 to 1.8; fructose 2,6-P2, 6 to 11.7; and fructose 1,6-P2, 7 micromolar, respectively.Fructose 2,6-P2 is known to occur in both plant and animal tissues at changing levels encompassing the K. values found in this studr, hence, these results implicate fructose 2,6-P2 as a natural activator of phosphoglucomutase, particularly in plants. Also, glucose 1,6-P2 has not been found in plants, and the method for measuring glucose 1,6-P2 by monitoring the activation of phosphoglucomutase is not specific.

Fructose 2,6-Bisphosphate Inhibition of Phosphoglucomutase

“…Conflicting results have been reported as to the effect of Fru 2,6-P2 on the enzyme PGM. While some investigators have reported an inhibition of PGM by Fru 2,6-P2 (1, 4), we have reported a stimulation (7). PGM, the enzyme responsible for the interconversion of Glc 1-P and Glc 6-P, occupies a central position in the pathway of sugar metabolism.…”

Effects of Fructose 2,6-Bisphosphate on Phosphoglucomutase from Plants

“…However, it has been recently reported that phosphoglucomutase from pea and mung bean, in the absence of glu-1,6-P2, is activated by fru-2,6-P2 (5 MATERIALS AND METHODS Chemicals. Glucose 1-P, glucose 6-P, glu-1 ,6-P2, fructose 6-P, fructose 1,6-P2, glycerate 3-P, glycerate 2,3-P2, NADP, ATP, glucose 6-P dehydrogenase from yeast, and phosphoglucomutase from rabbit muscle were obtained from Boehringer.…”

Photosynthate Metabolism in the Source Leaves of N2-Fixing Soybean Plants

“…Authentic glucose-1,6-bisP was obtained from Sigma. Reaction mixture conditions for soybean leaf PGM were established experimentally in this laboratory using modifications of previously decribed procedures (9,19,29). Preparations of freshly extracted PGM from animal tissues do not require glucose-1,6-bisP as a cofactor, as long as the enzyme remains phosphorylated (9).…”

“…Reaction mixture conditions for soybean leaf PGM were established experimentally in this laboratory using modifications of previously decribed procedures (9,19,29). Preparations of freshly extracted PGM from animal tissues do not require glucose-1,6-bisP as a cofactor, as long as the enzyme remains phosphorylated (9). In contrast, green plant PGM is not phosphorylated in vivo, and requires glucose-1,6-bisP as an obligate cofactor (9,29).…”

“…Preparations of freshly extracted PGM from animal tissues do not require glucose-1,6-bisP as a cofactor, as long as the enzyme remains phosphorylated (9). In contrast, green plant PGM is not phosphorylated in vivo, and requires glucose-1,6-bisP as an obligate cofactor (9,29). We now report that soybean leaf PGM also required glucose-1,6-bisP to support activity, and PGM activities in leaf extracts from all treatments were negligible in the absence of that cofactor (Fig.…”