Tyr140 and Lys212 are required for catalytic activity, Tyr140 is the general acid that protonates the substrate after decarboxylation, Lys212 lowers as a positively charged residue the pK of the nearby ionizable group in the enzyme-substrate complex and stabilizes the carbanion formed initially on substrate decarboxylation
active site structure and reaction mechanism, conformational changes at the active site resulting in closed and open forms, regulatory residues are isocitrate-binding Asp279and Ser94
overall reaction, catalytic mechanism, overview. The catalysis proceeds in three steps: (1) NADP+ reduction by the isocitrate substrate with the help of the Lys212B base, (2) beta-decarboxylation of the resulting oxalosuccinate, generating an enolate, and (3) protonation of this intermediate by Tyr139A, giving rise to the 2-oxooglutarate product. The beta-decarboxylation of oxalosuccinate is the most likely rate-limiting step. Role of Mg2+ and Asp275A, whose acid/base properties throughout the catalytic cycle lower the barrier to physiologically competent values. The catalysis takes place in a closed-conformation quaternary complex and involves significant conformational changes as the divalent metal (Mg2+ or Mn2+), the NADP+ cofactor, and the trianionic form of the isocitrate substrate (ICT) sequentially bind