title: Determination of molecular weight and molecular structure of rat-liver pyruvate carboxylase.
abstract: The molecular weight of pyruvate carboxylase isolated from pigeon and rat liver mitochondria was examined using analytical ultracentrifugation and electron microscopy. The enzyme molecule appeared as a tetramer with the four subunits arranged at the corners of a square. Sedimentation studies in the analytical ultracentrifuge, extrapolated to infinite dilution, showed the tetramer to have a molecular weight Mc=0r of 280 000 and an So20,w of 12.7 S. The tetramer could be dissociated into trimers and dimers of lower specific enzymic activity by storage at 4 degrees C or incubation at -- 20 degrees C at low protein concentrations. The isolated trimers and dimers had a molecular weight Mc=0r of 210 000 and 140 000, respectively, and an So20,w of 10.85 S and 7.55 S, respectively. Incubation with 2 M urea at 20 degrees C yielded enzymically inactive subunits (Mc=0r = 70 000; So20,w = 4.95 S). The molecular weights (for pyruvate carboxylase and its subunits), as calculated from the subunit diameter observed in the electron microscope, were consistent with the values obtained from sedimentation studies.
mesh_terms: D000818:Animals; D004355:Drug Stability; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D008297:Male; D008854:Microscopy, Electron; D008970:Molecular Weight; D011485:Protein Binding; D011487:Protein Conformation; D011766:Pyruvate Carboxylase / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D013696:Temperature; D014461:Ultracentrifugation
chemical_list: D046911:Macromolecular Substances; D011766:Pyruvate Carboxylase