title: Detailed kinetics and regulation of mammalian NAD-linked isocitrate dehydrogenase.
abstract: A mathematical model is presented to describe the catalytic mechanism of mammalian NAD-linked isocitrate dehydrogenase (NAD-IDH), a highly regulated enzyme in the tricarboxylic acid cycle, a crucial pathway in energy metabolism and biosynthesis. The mechanism accounts for allosteric regulation by magnesium-bound isocitrate and EGTA and calcium-bound ATP and ADP. The developed model is used to analyze kinetic data for the cardiac enzyme and to estimate kinetic parameter values. Since the kinetic mechanism is expressed in terms of chemical species (rather than biochemical reactants), the model explicitly accounts for the effects of biochemical state (ionic strength, pH, temperature, and metal cation concentration) on the kinetics. Because the substrate isocitrate competes with allosteric activators (ATP and ADP) and an inhibitor (EGTA) for metal ion cofactors (Ca(2+) and Mg(2+)), the observed kinetic relationships between reactants, activator and inhibitor concentrations, and catalytic flux are complex. Our analysis reveals that under physiological conditions, the ADP/ATP ratio plays a more significant role than Ca(2+) concentration in regulating the enzyme's activity. In addition, the enzyme is highly sensitive to Mg(2+) concentration in the physiological range, pointing to a potential regulatory role of [Mg(2+)] in mitochondrial energy metabolism.
authors.affiliation: Biotechnology and Bioengineering Center and Department of Physiology, Medical College of Wisconsin, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Qi
authors.forename: Xuewen
authors.initials: X
authors.lastname: Chen
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Beard
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D019295:Computational Biology; D004734:Energy Metabolism / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D007521:Isocitrate Dehydrogenase / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008322:Mammals / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D008956:Models, Chemical
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007521:Isocitrate Dehydrogenase; D008274:Magnesium; D002118:Calcium