Manganese(II) activation of 3-phosphoglycerate mutase of Bacillus megaterium: pH-sensitive interconversion of active and inactive forms.

The effects of manganese(II) ions and of pH were studied on 3-p-glycerate mutase purified from Bacillus megaterium. Mn2+ ions converted the enzyme within a few minutes from a catalytically inactive form to one that was catalytically active even after Mn2+ had been removed. The enzyme reverted over 60-90 min to the inactive form, from which further activation-deactivation cycles could be elicited. The slow, temperature-dependent, activation, and deactivation is suggestive of change in protein conformation. No other metal ion was found that activated more than 4% as much as Mn2+. Activation by Mn2+ was strongly pH-dependent in the physiological pH range, consistent with displacement of 2 H+. Together with the pH dependence of the catalytic activity itself, the system displayed pronounced pH sensitivity in the pH range 6.5-8.0. The findings suggest that pH changes, documented for forming and germinating spores of B. megaterium, can account for much of the mutase control associated with accumulation and later utilization of 3-phosphoglycerate depots.