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 bacteria are governed by the antagonistic activities of cDPG synthetase and cDPG hydrolase. In this paper we focus on the synthetase from Methanobacterium thermoautotrophicum. The cytoplasmic 150 kDa enzyme catalyzed 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, the 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 reaction proceeded with maximal rate at pH 6 and at 65 degrees C and was specifically dependent on high (> 0.3 M) K+ concentrations. The reaction conditions remarkably contrasted to those of cDPG degradation catalyzed by the previously described membrane-bound cDPG hydrolase.