Enzyme reactions cooperative phenomena

The book is organized in nine chapters and eleven appendices. Chapters 1 and 2 introduce the fundamental concepts and definitions. Chapters 3 to 7 treat binding systems of increasing complexity. The central chapter is Chapter 4, where all possible sources of cooperativity in binding systems are discussed. Chapter 8 deals with regulatory enzymes. Although the phenomenon of cooperativity here is manifested in the kinetics of enzymatic reactions, one can translate the description of the phenomenon into equilibrium terms. Chapter 9 deals with some aspects of solvation effects on cooperativity. Here, we only outline the methods one should use to study solvation effects for any specific system. 

Figure 5. Saturation kinetics the dependence of enzyme catalysis on the concentration of substrate. Reaction velocity represents the rate at which product is formed. (A) shows a hyperbolic saturation curve for two hypothetical enzymes. One binds its substrate more tightly than the other and reaches saturation at lower substrate concentration. This enzyme has a lower value, the substrate concentration where the reaction is half of maximum. The other binds the substrate more loosely and reaches the same velocity but requires higher substrate concentrations. (B) shows hypothetical velocities for cooperative enzymes. Although more complex, these enzymes also show the phenomenon of saturation.

Not all enzymes show the simple hyperbolic dependence of rate of reaction on substrate concentration shown in Figure 2.8. Some enzymes consist of several separate protein chains, each with an active site. In many such enzymes, the binding of substrate to one active site causes changes in the conformation not only of that active site, but of the whole multi-subunit array. This change in conformation affects the other active sites, altering the ease with which substrate can bind to the other active sites. This is cooperativity — the different subunits of the complete enzyme cooperate with each other. Because there is a change in the conformation (or shape) of the enzyme molecule, the phenomenon is also called allostericity (from the Greek for different shape ), and such enzymes are called allosteric enzymes. 

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