Chapter 3
Enzymes and Enzymatic Sensors
3.1 General
Enzymes are protein compounds that are specifically structured to bind to and act on a substrate (reactant molecule) to convert it by a catalytic mechanism, that is, by lowering the activation energy of the reaction with no effect on the chemical equilibrium [1–4].
Enzyme-catalyzed reactions rely on the formation of an intermediate involving both a shape and structure match of the substrate with the active site on the enzyme (Figure 3.1). In the resulting complex, substrate conversion is facilitated by various means. Thus, the enzyme–substrate interaction can cause a key chemical bond in the substrate to become weaker and prone to further alteration. Furthermore, the enzyme provides favorable conditions for stabilizing a reaction intermediate and preventing its reconversion to the initial form. When more than one reactant is involved, the enzyme, by specific chemical bindings, can gather all of them in a state that stimulates the reaction to proceed. In some cases, the enzyme active site can shuttle particles such as electrons or hydrogen ions that are needed in the reaction. Although Figure 3.1 shows a single-substrate reaction, many enzyme reactions involve two or more reactants (cosubstrates).
Figure 3.1 Mechanism of enzyme-catalyzed substrate conversion. E is the enzyme, S is the substrate, P1 and P2 are product. The intermediate state is an enzyme–substrate complex.
Enzymatic methods are widely used in bioanalytical chemistry ...
