On the influence of interprotein contacts on the active centers and catalytic properties of oligomeric enzymes

The results of structural and kinetic studies of the dissociative inactivat ion of oligomeric enzymes are discussed. The dissociative inactivation is t he process in which a kinetically irreversible protein change is preceded b y the reversible dissociation of oligomers. In experiments, this is demonst rated by the dependence of the inactivation rate on the total protein conce ntration. Relations that allow experimental data to be used for calculating the rate constant for the irreversible change of a monomeric protein, the equilibrium constant For dimer dissociation, and the rate constant for dime r dissociation were obtained. Conformational lock is the contact between pr otein globules in oligomeric enzymes that admits multistep destruction of a ctive oligomers and explains the induction period of thermal inactivation. The X-ray structural analyses performed for several dimeric and tetrameric enzymes explain why proteins lose their catalytic activity during the disso ciation to monomers and give a physically reasonable picture of the structu re of the conformational lock in oligomeric enzymes. These data lend suppor t to the kinetic schemes used in kinetic experiments.