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 REGULATORYPROPERTIES())

The hyperthermophilic archaeum Thermoproteus tenax possesses two glyce raldehyde-3-phosphate dehydrogenases differing in cosubstrate specific ity and phosphate dependence of the catalyzed reaction, NAD(+)- depend ent glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphate-i ndependent irreversible oxidation of D-glyceraldehyde 3-phosphate to 8 -phosphoglycerate, The coding gene was cloned, sequenced, and expresse d in Escherichia coli, Sequence comparisons showed no similarity to ph osphorylating glyceraldehyde-3-phosphate dehydrogenases but revealed a relationship to aldehyde dehydrogenases, with the highest similarity to the subgroup of nonphosphorylating glyceraldehyde-3-phosphate dehyd rogenases. The activity of the enzyme is affected by a series of metab olites, All effecters tested influence the affinity of the enzyme for its cosubstrate NAD(+), Whereas NADP(H), NADH, and ATP reduce the affi nity for the cosubstrate, AMP, ADP, glucose 1-phosphate, and fructose 6-phosphate increase the affinity for NAD(+), Additionally, most of th e effecters investigated induce cooperativity of NAD(+) binding. The i rreversible catabolic oxidation of glyceraldehyde 3-phosphate, the con trol 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 co nstituent of glycolysis in T, tenax. Its regulatory properties substit ute for those lacking in the reversible nonregulated pyrophosphate-dep endent phosphofructokinase in this variant of the Embden-Meyerhof-Parn as pathway.