Aspartate dehydrogenase, NAD biosynthesis <p>This group contains aspartate dehydrogenases that belong to a unique class of amino aciddehydrogenases.</p> <p>The structure of <taxon tax_id="2336">Thermotoga maritima</taxon> TM1643 has been found tocontain an N-terminal Rossmann fold domain (which binds the NAD(⁺) cofactor) and a C-terminalalpha/beta domain [<cite idref="PUB00014412"/>]. This suggested that TM1643 may be a dehydrogenase with the activesite located at the interface between the two domains. Enzymatic characterisation of TM1643 revealed that itpossesses NAD or NADP-dependent dehydrogenase activity toward l-aspartate but no aspartate oxidase activity[<cite idref="PUB00014412"/>]. The product of the aspartate dehydrogenase activity is also iminoaspartate. It hasbeen suggested that two different enzymes, an oxidase and a dehydrogenase, may have evolved to catalyse thefirst step of NAD biosynthesis [<cite idref="PUB00014412"/>]. Members of this group share some structuralsimilarity to several other NAD(P)⁺-dependent oxidoreductases, including inositol 1-phosphatesynthase, dihydrodipicolinate reductase, and ASA-DH [<cite idref="PUB00014412"/>].</p> <p>It has been proposed thatin <taxon tax_id="2336">Thermotoga maritima</taxon>, TM1643 catalyses the first reaction of de novo biosynthesisof NAD from aspartate, and it produces iminoaspartate required for this pathway. The formation of an enzymecomplex between TM1643 and NadA, the next enzyme of the pathway, may allow the channeling of this unstableproduct directly to the NadA active site [<cite idref="PUB00014412"/>].</p> <p>The same domain is present in animals(e.g., <taxon tax_id="6239">Caenorhabditis elegans</taxon> F17C8.3 protein).</p>