ACTIVATION AND THERMOSTABILIZATION EFFECTS OF CYCLIC 2,3-DIPHOSPHOGLYCERATE ON ENZYMES FROM THE HYPERTHERMOPHILIC METHANOPYRUS-KANDLERI

Enzymes involved in methane formation from carbon dioxide and dihydrog en in Methanopyrus kandleri require high concentrations (> 1 M) of lyo tropic salts such as K2HPO4/KH2PO4 or (NH4)(2)SO4 for activity and for thermostability. The requirement correlates with high intracellular c oncentrations of cyclic 2,3-diphosphoglycerate (cDPG; approximate to 1 M) in this hyperthermophilic organism. We report here on the effects of potassium cDPG on the activity and thermostability of the two metha nogenic enzymes cyclohydrolase and formyltransferase and show that at cDPG concentrations prevailing in the cells the investigated enzymes a re highly active and completely thermostable. At molar concentrations also the potassium salts of phosphate and of 2,3-bisphosphoglycerate, the biosynthetic precursor of cDPG, were found to confer activity and thermostability to the enzymes. Thermodynamic arguments are discussed as to why cDPG, rather than these salts, is present in high concentrat ions in the cells of Mp. kandleri.