Cooperativity in Enzyme Catalysis

This chapter presents the concept of cooperative interactions between distal binding sites on oligomeric enzymes, which communicate through conformational transitions of the polypeptide chain. These allosteric enzymes display deviations from the normal Henri–Michaelis–Menten behavior that is seen with single substrate binding enzymes. The chapter also presents examples of allosteric proteins and enzymes that provide some structural rationale for allosteric interactions in specific cases, and describes two theoretical models of cooperativity. The proteins hemoglobin and the Trp repressor provide good examples of the concepts of ligand cooperativity and allosteric regulation, respectively. The appearance of sigmoidal kinetics in enzyme velocity curves for allosteric enzymes reflects the cooperativity of the substrate binding events that precede the catalytic steps at the enzyme active sites. The same cooperativity should be realized in direct studies of ligand binding by the enzyme, which can be performed by equilibrium dialysis, certain spectroscopic methods, and so on.