title: Dissociation of aspartate aminotransferase into subunits. Effect of ligands upon this dissociation.
abstract: Frontal and zonal analysis of the chromatography of aspartate aminotransferase (EC2.61.1), pig heart cytosolic enzyme, on Bio-Gel P150 shows that holo- and apoenzyme can dissociate at pH 8.3. Ultracentrifugation and fluorescence depolarization confirm this result. Kinetic analysis of the fluorescence depolarization experiments favors a biphasic phenomenon: a few minutes for the faster one and several hours for the slower one. The apparent dissociation constant is 0.8 muM for the apoenzyme and 0.18 muM for the pyridoxal 5'-phosphate form of the holoenzyme. In the presence of sucrose or 0.1 M L-aspartate or a mixture of 70 mM L-glutamate and 2 mM alpha-ketoglutarate, the holoenzyme is dimeric at concentrations higher than 5 nM. The addition of a mixture of the substrates L-glutamate and alpha-ketoglutarate to a monomeric holoenzyme leads to dimerization. The stability of the dimeric form is in the order: holoenzyme + substrates greater than apoenzyme.
mesh_terms: D001219:Aspartate Aminotransferases / Q000378:metabolism; D001665:Binding Sites; D008024:Ligands; D046911:Macromolecular Substances; D008433:Mathematics; D008970:Molecular Weight; D011485:Protein Binding; D011487:Protein Conformation; D011732:Pyridoxal Phosphate; D013050:Spectrometry, Fluorescence
chemical_list: D008024:Ligands; D046911:Macromolecular Substances; D011732:Pyridoxal Phosphate; D001219:Aspartate Aminotransferases