Evidence for the operation of a novel Embden-Meyerhof pathway that involves ADP-dependent kinases during sugar fermentation by Pyrococcus furiosus

Abstract

The main pathway for the fermentation of maltose or cellobiose by the hyperthermophile Pyrococcus furiosus was investigated by in vivo NMR and by enzyme measurements. Addition of [1-13C]glucose to cell suspensions resulted in the formation of C2-labeled acetate and C3-labeled alanine. No label was recovered in CO2 or HCO3-. In the presence of [3-13C]glucose, the label ended up in the C1 atom of alanine and in HCO3- and CO2. These labeling patterns indicate that glucose is converted along an Embden-Meyerhof pathway, and they disagree with the previously proposed nonphosphorylated Entner-Doudoroff pathway (pyroglycolysis). The NMR data were supported by enzyme measurements. Hexokinase (8.7 units/mg), phosphoglucose isomerase (6.8 units/mg), phosphofructokinase (0.81 unit/mg), and aldolase (0.26 unit/mg) were present in cell-free extracts (specific activities at 90 degrees C). Remarkably, the two kinases required ADP as the phosphoryl group donor instead of ATP. No activity was found with pyrophosphate. These are the first descriptions of ADP-dependent (AMP-forming) kinases to date. Since P. furiosus is a phylogenetically ancient organism, these enzymes may represent an ancestral kind of metabolism.