Regulation of Enzyme Reactions

Rates of enzyme reactions are often affected by the presence of various chemicals and ions. Enzyme inhibitors combine, either reversibly or irreversibly, with enzymes and cause a decrease in enzyme activity. Effectors control enzyme reactions by combining with the regulatory site(s) of enzymes. There are several mechanisms of reversible inhibition and for the control of enzyme reactions. 

Competitive Inhibition An inhibitor competes with a substrate for the binding site of an enzyme. As an enzyme-inhibitor complex does not contribute to product formation, it decreases the rate of product formation. Many competitive inhibitors have steric structures similar to substrates, and are referred to as substrate analogs. 

Product inhibition is another example of such an inhibition mechanism of enzyme reactions, and is due to a structural similarity between the substrate and the product. The mechanism of competitive inhibition in a unimolecular irreversible reaction is considered as follows  

The sum of the concentrations of the remaining enzyme Cp and its complexes, Cp and Cpp should be equal to its initial concentration Cp,. 

If the rates of formation of the complexes EA and El are very fast, then the following two equilibrium relationships should hold  

---