[Kinetic properties of the alpha-ketoglutarate dehydrogenase complex from pigeon breast muscle]

A complex kinetic behaviour of the alpha-ketoglutarate dehydrogenase component isolated from the pigeon breast muscle alpha-ketoglutarate dehydrogenase complex was established. The dependence curve of the reaction rate versus substrate concentration has an intermediate plateau and a maximum. The shape of the kinetic curve and specific activity depend on the enzyme concentration both in the reaction mixture and in the original solution of enzyme. The kinetic pattern of isolated alpha-ketoglutarate dehydrogenase suggests that the enzyme is a multi-step dissociating system characterized by different rates of oligomeric forms interconversions at various steps of dissociation. It is assumed that the process of alpha-ketoglutarate dehydrogenase oligomerization is a cooperative one. The kinetic behaviour of the complex and its constituent alpha-ketoglutarate dehydrogenase component is characterized by the same type of the v + [S] dependence curves as is the isolated enzyme. The correlation between the kinetic properties of the enzyme complex and its alpha-ketoglutarate dehydrogenase component and the kinetic behaviour of free alpha-ketoglutarate dehydrogenase suggest that the association-dissociation processes which are probably typical for the component within the complex determine the kinetic behaviour of the complex to a large extent. It is assumed that the anomalous kinetic behaviour of the alpha-ketoglutarate dehydrogenase component is due to the cooperative effects during substrate binding, which are mediated by a shift in the equilibrium between the oligomeric forms of enzyme.