Enzyme Kinetics

Enzymes are naturally occurring biological catalysts that are extremely efficient and specific. Enzymes accelerate the rate of a reaction by factors of at least a million as compared to the same reaction without the enzyme. Most biological reaction rates are not perceivable in the absence of the enzyme. The term enzyme was first used by a German pshysiologist Wilhelm Kühne in 1897. There are over 700 different kinds of enzymes that have been identified. Enzymes can be classified into several categories such as hydrolytic, oxidizing, and reducing. One of the simplest biological reactions by an enzyme is the breaking down of hydrogen peroxide by the enzyme catalase. This reaction is a very essential life process since the metabolic waste product, hydrogen peroxide, is toxic to the cell in high amounts. Catalase is a very efficient enzyme, it has one of the highest rates of reaction among all of the enzymes. Enzymes have high specificity, generally enzymes catalyse only a single chemical reaction or a set of closely related chemical reactions. Enzymes do not affect the products of the reactions they catalyze, they only hastens the reaction process.

Figure 1. Diagram showing the energy required on catalyzed and uncatalyzed reactions

Enzymes technically lowers the energy of activation of the reactions thus increasing the rate at which the reactions take place (Fig. 1). Catalase is an enzyme capable of speeding up the breakdown of hydrogen peroxide into water and oxygen gas. Enzyme activity is affected by many factors such as temperature, pH, concentration of enzyme and substrate, and lastly is the presence of inhibitor. Inhibitors act to slow down or even stop the action of the enzymes. Inhibitors are generally categorized as competitive and non-competitive. Competitive inhibitors bind to the active site of the enzyme rendering the substrate unable to bind to the enzyme and hindering the reaction to take place. Non-competitive inhibitors on the other hand bind to the allosteric site of the enzyme, changing the enzyme’s conformation and deactivating the enzyme. In this experiment, the effect of inhibitors on the enzyme activity is also studied. There are several ways of determining the enzymatic catalysis of enzymes such as MichaelisMenten model, Lineweaver-Burk plot, and Eadie-Hofstee model. Michaelis–Menten model is a simple

model used in enzyme kinetics. The model is an equation that describes the rate of enzymatic reactions by relating the reaction rate to the concentration of the substrate. The equation is given by:

Eadie-Hofstee model on the other hand is a graphical representation of enzyme kinetics wherin reaction velocity is plotted as a function of the ratio between substrate concentration and reaction velocity. The equation is as follows:

Enzyme kinetics can also be represented graphically using the Lineweaver-Burk plot. It uses a formula also derived from the Michaelis-Menten equation. The formula in Lineweaver-Burk method is as follows:

In all of the above equations, v is the reaction rate S is the concentration of the substrate. Vmax is the maximum rate that can be reached by the system when it is saturated with the substrate. K m or the Michaelis constant is the concentration of the substrate at half the Vmax.

Reference: Campbell, M. K., & Farrell, S. O. Biochemistry. 7th Edition. Brooks/Cole Cengage Learning. China: 2009