| Abstract: | The large depot of phosphoglyceric acid (PGA) which is accumulated within spores of Bacillus megaterium is greater than 99% 3-phosphoglyceric acid (3-PGA). The 3-PGA depot is stable in forespores and dormant spores, but is utilized rapidly during spore germination. When spores were germinated in KBr plus NaF, the PGA depot was not utilized, but 13% of the 3-PGA was converted to 2-PGA. These data suggest phosphoglycerate phosphomutase as the enzyme which is regulated to allow 3-PGA accumulation during sporulation. Young isolated forespores, in which 3-PGA was normally stable, utilized their 3-PGA rapidly when incubated with Mn2+ plus the divalent cation ionophore X-537A; Mn2+ or ionophore alone or Mg2+ or Ca2+ plus ionophore was without effect. Young forespores contained significant amounts of Mn2+. However, forespore Mn2+ exchanged slowly with exogenous Mn2+ and was removed poorly by toluene treatment. This suggests that much of the forespore Mn2+ is tightly bound to some forespore component. Since phosphoglycerate phosphomutase from B. megaterium has an absolute and specific requirement for Mn2+, these data suggest that the activity of this enzyme in vivo may be regulated to a large degree by the level of free Mn2+. Indeed, the activity of this enzyme in forespore or dormant spore extracts was stimulated greater than 25-fold by Mn2+, whereas comparable extracts from cells or germinated spores were stimulated only two- to fourfold. |
