COMPARATIVE-ANALYSIS OF EMBDEN-MEYERHOF AND ENTNER-DOUDOROFF GLYCOLYTIC PATHWAYS IN HYPERTHERMOPHILIC ARCHAEA AND THE BACTERIUM THERMOTOGA

The Embden-Meyerhof (EM) or Entner-Doudoroff (ED) pathways of sugar de gradation were analyzed in representative species of the hyperthermoph ilic archaeal genera Thermococcus, Desulfurococcus, Thermoproteus, and Sulfolobus, and in the hyperthermophilic (eu)bacterial genus Thermoto ga. The analyses included (1) determination of C-13-labeling patterns by H-1- and C-13-NMR spectroscopy of fermentation products derived fro m pyruvate after fermentation of specifically C-13-labeled glucose by cell suspensions, (2) identification of intermediates of sugar degrada tion after conversion of C-14-labeled glucose by cell extracts, and (3 ) measurements of enzyme activities in cell extracts. Thermococcus cel er and Thermococcus litoralis fermented C-13-glucose to acetate and al anine via a modified EM pathway (100%). This modification involves ADP -dependent hexokinase, 6-phosphofructokinase, and glyceraldehyde-3-pho sphate:ferredoxin oxidoreductase (GAP:FdOR). Desulfurococcus amylolyti cus fermented C-13-glucose to acetate via a modified EM pathway in whi ch GAP:FdOR replaces GAP-DH/phosphoglycerate kinase. Thermoproteus ten ax fermented C-13-glucose to low amounts of acetate and alanine via si multaneous operation of the EM pathway (85%) and the ED pathway (15%). Aerobic Sulfolobus acidocaldarius fermented C-13-labeled glucose to l ow amounts of acetate and alanine exclusively via the ED pathway. The anaerobic (eu)bacterium Thermotoga maritima fermented C-13-glucose to acetate and lactate via the EM pathway (85%) and the ED pathway (15%). Cell extracts contained glucose-6-phosphate dehydrogenase and 2-keto- 3-deoxy-6-phosphogluconate aldolase, key enzymes of the conventional p hosphorylated ED pathway, and, as reported previously, all enzymes of the conventional EM pathway. In conclusion, glucose was degraded by hy perthermophilic archaea to pyruvate either via modified EM pathways wi th different types of hexose kinases and GAP-oxidizing enzymes, by the nonphosphorylated ED pathway, or by a combination of both pathways. I n contrast, glucose catabolism in the hyperthermophilic (eu)bacterium Thermotoga involves the conventional forms of the EM and ED pathways. The data are in accordance with various previous reports.