Cooperative Manganese(II) Activation of 3-Phosphoglycerate Mutase of Bacillus megaterium: A Biological pH-Sensing Mechanism in Bacterial Spore Formation and Germination

The conversion of 3-P-glycerate mutase of Bacillus megaterium from a catalytically inactive to an active form was markedly more effective with buffered Mn2+ than with just added Mn2+. The previously reported stimulation by threonine disappeared when buffered Mn2+ was used. Activation of mutase showed a sigmoid dependence on Mn2+ concentration when buffered with tetramethylenediamine tetraacetate. The curve obeyed Hill kinetics with a coefficient of 2.1 ± 0.1. At 0.5 μM free Mn2+, buffered with trimethylenediamine tetraacetate, activation of mutase increased about 73-fold over the pH range 6.6 to 7.4, Plotted against [OH−], the activation showed a strongly sigmoid response with Hill coefficient of 3.5 ± 0.1. When mutase activated at pH 6.4 and 0.5 μM free Mn2+ in the presence of substrate was transferred to a similar medium at pH 7.4, the rate of product accumulation increased 360-fold within a few minutes. The pH sensitivity conferred upon mutase by low [Mn2+] may account for its large activity decrease during sporulation, and later increase during spore germination, when spore pH, respectively, declines and rises by about 1 unit. These changes result in the accumulation, and later reutilization, of 3-P-glycerate reserves in the spore. Such a pH-sensing function of Mn2+ may have wider biological uses.