NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase from Thermoproteus tenax -: The first identified archaeal, member of the aldehyde dehydrogenase superfamily is a glycolytic enzyme with unusual regulatory properties

The hyperthermophilic archaeum Thermoproteus tenax possesses two glyceraldehyde-3-phosphate dehydrogenases differing in cosubstrate specificity and phosphate dependence of the catalyzed reaction, NAD(+)- dependent glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphate-independent irreversible oxidation of D-glyceraldehyde 3-phosphate to 8-phosphoglycerate, The coding gene was cloned, sequenced, and expressed in Escherichia coli, Sequence comparisons showed no similarity to phosphorylating glyceraldehyde-3-phosphate dehydrogenases but revealed a relationship to aldehyde dehydrogenases, with the highest similarity to the subgroup of nonphosphorylating glyceraldehyde-3-phosphate dehydrogenases. The activity of the enzyme is affected by a series of metabolites, All effecters tested influence the affinity of the enzyme for its cosubstrate NAD(+), Whereas NADP(H), NADH, and ATP reduce the affinity for the cosubstrate, AMP, ADP, glucose 1-phosphate, and fructose 6-phosphate increase the affinity for NAD(+), Additionally, most of the effecters investigated induce cooperativity of NAD(+) binding. The irreversible catabolic oxidation of glyceraldehyde 3-phosphate, the control of the enzyme by energy charge of the cell, and the regulation by intermediates of glycolysis and glucan degradation identify the NAD(+)-dependent glyceraldehyde-3-phosphate dehydrogenase as an integral constituent of glycolysis in T, tenax. Its regulatory properties substitute for those lacking in the reversible nonregulated pyrophosphate-dependent phosphofructokinase in this variant of the Embden-Meyerhof-Parnas pathway.