Alanine dehydrogenase catalyses the NAD-dependent reversible reductive amination of pyruvate into alanine. Pyridine nucleotide transhydrogenase catalyses 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 … expand

Alanine dehydrogenase catalyses the NAD-dependent reversible reductive amination of pyruvate into alanine. Pyridine nucleotide transhydrogenase catalyses 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 alpha chain (gene pntA) and a beta chain (gene pntB), while in eukaryotes it is a single chain protein.

The sequence of alanine dehydrogenase from several bacterial species is related to the alpha subunit of bacterial pyridine nucleotide transhydrogenase and the N-terminal half of the eukaryotic enzyme. The two most conserved regions correspond respectively to the N-terminal domain of these proteins, represented in this entry, and to a central glycine-rich domain which is part of the NAD(H)-binding site [ PUBMED:8439307 ]. The N-terminal domain is also found in lysine 2-oxoglutarate reductases [ PUBMED:11354603 ].