title: Subunit dissociation of mitochondrial malate dehydrogenase.
abstract: Fluorescence polarization studies of porcine mitochondrial malate dehydrogenase labeled with fluorescein isothiocyanate or fluorescamine indicated a concentration-dependent dissociation of the dimeric molecule with a KD OF 2 X 10(7) N at pH 8.0. These results were confirmed by the concentration dependence of the stability of the enzyme at elevated temperatures and the creation of hybrid molecules with fluorescein and Rhodamine B labeled subunits, in which energy transfer was observed. The binding of NADH resulted in a small shift of the subunit dissociation curve toward monomer, demonstrating that monomer has twice the affinity for reduced coenzyme. NAD+ binding prevented dissociation of the dimer, even at concentrations below 10(-8) N. These results indicate that binding of reduced or oxidized coenzymes results in different conformation changes, which are transferred to the subunit interface.
mesh_terms: D000818:Animals; D004355:Drug Stability; D004735:Energy Transfer; D005450:Fluorescamine; D005452:Fluoresceins; D046911:Macromolecular Substances; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D012235:Rhodamines; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D005452:Fluoresceins; D046911:Macromolecular Substances; D012235:Rhodamines; D009243:NAD; D005450:Fluorescamine; D008291:Malate Dehydrogenase