Alanine dehydrogenase and pyridine nucleotide transhydrogenase signatures

The following dehydrogenases have been shown [1] to share regions of similarity:

• Alanine dehydrogenase (EC 1.4.1.1), an enzyme which catalyzes the NAD- dependent reversible reductive amination of pyruvate into alanine.
• Pyridine nucleotide transhydrogenase (EC 1.6.1.1), which is the enzyme that catalyzes the reduction of NADP+ to NADPH with the concomitant oxidation of NADH to NAD+. This enzyme is located in the plasma membrane of prokaryotes and in the inner membrane of the mitochondria of eukaryotes. The transhydrogenation between NADH and NADP is coupled with the translocation of a proton across the membrane. In prokaryotes the enzyme is composed of two different subunits: an α chain (gene pntA) and a β chain (gene pntB) while in eukaryotes it is a single chain protein.

The sequence of alanine dehydrogenase from several bacterial species are related with those of the α subunit of bacterial pyridine nucleotide transhydrogenase and of the N-terminal half of the eukaryotic enzyme. The two most conserved regions correspond respectively to the N-terminal extremity of these proteins and to a central glycine-rich region which is part of the NAD(H)-binding site. We have developed signature patterns for both regions.