CYCLIC 2,3-DIPHOSPHOGLYCERATE METABOLISM IN METHANOBACTERIUM-THERMOAUTOTROPHICUM (STRAIN DELTA-H) - CHARACTERIZATION OF THE SYNTHETASE REACTION

The levels of cyclic 2,3-diphosphoglycerate (cDPG) in methanogenic bac teria are governed by the antagonistic activities of cDPG synthetase a nd cDPG hydrolase. In this paper we focus on the synthetase from Metha nobacterium thermoautotrophicum. The cytoplasmic 150 kDa enzyme cataly zed cDPG synthesis from 2,3-diphosphoglycerate (apparent K-m = 21 mM), Mg2+ (K-m = 3.1 mM) and ATP (K-m = 1-2 mM). In batch-fed cultures, th e enzyme was constitutively present (6-6.5 nmol per min per mg protein ) during the different growth phases. In continuous cultures, activity decreased in response to phosphate limitation. The synthetase reactio n proceeded with maximal rate at pH 6 and at 65 degrees C and was spec ifically dependent on high (> 0.3 M) K+ concentrations. The reaction c onditions remarkably contrasted to those of cDPG degradation catalyzed by the previously described membrane-bound cDPG hydrolase.