Cyclic 2,3-diphosphoglycerate as a component of a new branch in gluconeogenesis in Methanobacterium thermoautotrophicum delta

A unique compound, cyclic 2,3-diphosphoglycerate (cDPG), is the major soluble carbon and phosphorus solute in Methanobacterium thermoautotrophicum AH under optimal conditions of cell growth. It is a component of an unusual branch in gluconeogenesis in these bacteria. [U-13Clacetate pulse-[12C]acetate chase methodology was used to observe the relationship between cDPG and other metabolites (2-phosphoglycerate and 2,3-diphosphoglycerate [2-PG and 2,3-DPG, respectively]) of this branch. It was demonstrated that cells could grow exponentially under conditions in which 2-PG and 2,3-DPG, rather than cDPG, were the major solutes. While the total concentration of these three phosphorylated molecules was maintained, rapid interconversion of 13C label among them was observed. Label flow from 2-PG to 2,3-DPG to cDPG to polymer is the usual direction in this pathway in exponentially growing cells, while the reverse reactions sometimes predominate in the stationary phase. Evidence of the presence of a polymeric compound in this pathway was provided by 13C nuclear magnetic resonance (one-dimensional and two-dimensional INADEQUATE) studies of solubilized cell debris. Methanogens are a very diverse group of the classArchae-obacteria able to generate energy by reducing a variety of substrates, including formate, acetate, methanol, mono-, di-