title: On the mechanism of NADP+-linked isocitrate dehydrogenase from heart mitochondria. I. The kinetics of dissociation of NADPH from its enzyme complex.
abstract: The kinetics of dissociation of NADPH from its complex with isocitrate dehydrogenase, and from the abortive complex of enzyme, Mg2+, isocitrate and NADPH, have been studied in phosphate and triethanolamine buffers by means of rapid fluorescence measurements. The reactions are complex, and it is suggested that a conformational equilibrium of each of the complexes is involved, and that this conformational change is also responsible for a slow approach to the steady-state rate of oxidative decarboxylation observed previously in triethanolamine buffer under certain conditions (K. Dalziel, N. McFerran, B. Matthews & C.H. Reynolds, Biochem. J. 171, 743-750 (1978) ). It is concluded that release of free NADPH product is not the rate-limiting step in oxidative decarboxylation in the steady state. The validity of the ligand displacement method used to measure the dissociation kinetics of the enzyme-NADPH complex has been studied by computer simulation.
mesh_terms: D000818:Animals; D002021:Buffers; D002417:Cattle; D004983:Ethanolamines / Q000378:metabolism; D007521:Isocitrate Dehydrogenase / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008929:Mitochondria, Heart / Q000201:enzymology*; D009249:NADP / Q000378:metabolism*; D009994:Osmolar Concentration; D010710:Phosphates / Q000378:metabolism
chemical_list: D002021:Buffers; D004983:Ethanolamines; D010710:Phosphates; D009249:NADP; D007521:Isocitrate Dehydrogenase; D008274:Magnesium