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Alanine dehydrogenase and related dehydrogenases Alanine dehydrogenase/Transhydrogenase, such as the hexameric L-alanine dehydrogenase of Phormidium lapideum, contain 2 Rossmann fold-like domains linked by an alpha helical region. Related proteins include Saccharopine Dehydrogenase (SDH), bifunctional lysine ketoglutarate reductase /saccharopine dehydrogenase enzyme, N(5)-(carboxyethyl)ornithine synthase, and Rubrum transdehydrogenase. Alanine dehydrogenase (L-AlaDH) catalyzes the NAD-dependent conversion of pyrucate to L-alanine via reductive amination. Transhydrogenases found in bacterial and inner mitochondrial membranes link NAD(P)(H)-dependent redox reactions to proton translocation. The energy of the proton electrochemical gradient (delta-p), generated by the respiratory electron transport chain, is consumed by transhydrogenase in NAD(P)+ reduction. Transhydrogenase is likely involved in the regulation of the citric acid cycle. Rubrum transhydrogenase has 3 components, dI, dII, and dIII. dII spans the membrane while dI and dIII protrude on the cytoplasmic/matirx side. DI contains 2 domains with Rossmann folds, linked by a long alpha helix, and contains a NAD binding site. Two dI polypeptides (represented in this sub-family) spontaneously form a heterotrimer with one dIII in the absence of dII. In the heterotrimer, both dI chains may bind NAD, but only one is well-ordered. dIII also binds a well-ordered NADP, but in a different orientation than classical Rossmann domains. |
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