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Structure
Human placental GapDH holoenzyme 1U8F — NAD⁺ bound in each subunit (Jenkins JL & Tanner JJ, Acta Crystallogr D 2006, PMID:16510976).
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① G3P enters — thiohemiacetal
[schematic] G3P (PubChem pose) meets the deprotonated catalytic Cys152 thiol, forming a covalent thiohemiacetal — the nucleophilic-cysteine mechanism that couples oxidation to phosphate transfer.
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② Hydride transfer → NADH
[schematic] The substrate C–H flips as hydride onto the NAD⁺ nicotinamide C4 while His179 helps; the thiohemiacetal becomes a high-energy thioester (the "energy bonus"), and NAD⁺ is reduced to NADH.
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③ Phosphorolysis → 1,3-BPG
[schematic] Inorganic phosphate attacks the thioester to release 1,3-bisphosphoglycerate; NADH departs carrying the reducing equivalents (NADH _pub pose, drawn schematically).
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Sequence
DNA/gene NCBI Gene 2597 · protein UniProt P04406
› Backbones and ligand poses are taken directly from the listed PDB entries,
superposed into one common frame. Where no crystalline state exists for a step
(e.g., Michaelis geometry), the pose is drawn schematically using PubChem 3D
geometries and is labeled as such in the narration.