Nicotinamide nucleotide transhydrogenase: a model for utilization of substrate binding energy for proton translocation

@article{Hatefi1996NicotinamideNT,
  title={Nicotinamide nucleotide transhydrogenase: a model for utilization of substrate binding energy for proton translocation},
  author={Youssef Hatefi and Mutsuo Yamaguchi},
  journal={The FASEB Journal},
  year={1996},
  volume={10},
  pages={444 - 452}
}
The energy‐transducing nicotinamide nucleotide transhydrogenases of mammalian mitochondria and bacteria are structurally related mem‐ brane‐bound enzymes that catalyze the direct transfer of a hydride ion between NAD(H) and NADP(H) in a reaction that is coupled to transmembrane proton translocation. The protonmotive force alters the affinity of the transhydrogenase for substrates, accelerates the rate of hydride ion transfer from NADH to NADP, and shifts the equilibrium of this reaction toward… 
The Proton Channel of the Energy-transducing Nicotinamide Nucleotide Transhydrogenase of Escherichia coli *
TLDR
It is proposed that the three helices bearing His-91, Ser-139, and Asn-222 come together, possibly with another highly conserved α helix to form a four-helix bundle proton channel and that Asp-213 serves to conduct protons between the channel and domain III where NADPH binding energy is used via protein conformation change to initiate outward proton translocation.
Crystal structure of transhydrogenase domain III at 1.2 Å resolution
TLDR
The crystal structure of the NADP(H) binding domain III of bovine TH is described and it is revealed that NADP is bound in a manner inverted from that previously observed for nucleotide binding folds.
Interactions between Transhydrogenase and Thio-nicotinamide Analogues of NAD(H) and NADP(H) Underline the Importance of Nucleotide Conformational Changes in Coupling to Proton Translocation*
TLDR
The finding that thio-NADP+ is a good substrate despite an increased Xam value shows that approach of the NADH prior to hydride transfer is not obstructed by the S atom in the analogue.
Fast Hydride Transfer in Proton-translocating Transhydrogenase Revealed in a Rapid Mixing Continuous Flow Device*
TLDR
At elevated NADH concentrations, the first-order rate constant of the reaction approaches 21,200 s−1, which is larger than that measured for redox reactions of nicotinamide nucleotides in other, soluble enzymes.
Essential Glycine in the Proton Channel of Escherichia coli Transhydrogenase*
TLDR
Gly252 mutants are distinguished by high levels of cyclic transhydrogenation activity in the absence of added NADP(H) and by complete loss of proton pumping activity, implying that Gly252 mutants exhibit a native-like domain II conformation while blocking proton translocation and coupled exchange of NADP (H) in domain III.
Division of labor in transhydrogenase by alternating proton translocation and hydride transfer
TLDR
The structures of the entire transhydrogenase enzyme and the membrane domain from the bacterium Thermus thermophilus are solved, suggesting a catalytic mechanism in which the two copies of dIII alternatively function in proton translocation and hydride transfer.
Evidence That the Transfer of Hydride Ion Equivalents between Nucleotides by Proton-translocating Transhydrogenase Is Direct*
TLDR
The molecular masses of the purified, recombinant nucleotide-binding domains (domains I and III) of transhydrogenase from Rhodospirillum rubrum were determined by electrospray mass spectrometry and indicated that the nicotinamide rings of the nucleotides are in close apposition during the hydride transfer reaction, and it imposes firm constraints on the mechanism by which transHydrogenation is linked to proton translocation.
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References

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TLDR
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TLDR
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