Modeling the Kinetics and Regulation of Mammalian 2‐Oxoglutarate Dehydrogenase

Mitochondrial 2‐oxoglutarate (α‐Ketoglutarate) dehydrogenase complex (OGDHC), a key regulatory point of tricarboxylic acid cycle, plays vital roles in the multiple pathways of energy metabolism and biosynthesis. The catalytic mechanism of OCDHC and the allosteric regulation of its activity have not been well understood due to the large and sophisticated protein assemblies inside this massive enzyme complex. We present here a mathematical model to describe the catalytic mechanism of OGDHC and the mechanisms accounting for allosteric regulations by EGTA, nucleotides (ATP, ADP), and metal ion cofactors (Ca 2+ , Mg 2+ ). The model is derived based on an ordered tri‐tri enzyme mechanism combined with the conformational changes associated with the rotation of one lipoic between three catalytic sites. The developed model is parameterized based on analyzing kinetic data sets from multiple sources and is further validated by independent data sets. The model adequately describes the experimentally observed kinetics of OGDHC and the regulatory effect of cofactors on the enzyme activity. The overall kinetic analysis demonstrates that the proposed mechanism, a hybrid rapid‐equilibrium ping‐pong random mechanism, is consistent with previously reported kinetic mechanism characteristics. The significances of regulation by different cofactors under physiological conditions are also discussed.