BIOLOGY Volume 1 - A Guide to General Biology - 2004

4. ENZYMES

4.3. Factors Affecting the Rate of Enzyme-Catalyzed Reactions

4.3.4. pH

At a constant Temperature, any enzyme typically operates most efficiently within a narrow pH range. The optimum pH is considered to be the value at which the reaction proceeds at its maximum rate (Fig. 4.10 and Table 4.1). At higher and lower pH values, enzyme activity decreases. As the pH drops, acidity increases along with the concentration of H⁺ ions. Consequently, the number of positive charges in the medium rises. A shift in pH alters the charge of ionized acidic and basic groups, which leads to the disruption of ionic bonds involved in maintaining the specific conformation of enzyme molecules (sec. 3.5.3). As a result, the shape of the enzyme molecules changes, most notably the shape of their Active Site. Extreme pH shifts will cause the enzyme to denature.

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Fig. 4.10. Effect of pH on The rate of an enzyme-catalyzed reaction.

Table 4.1. Optimum pH for various Enzymes

4.2. a) State the optimum pH for The activity of enzyme B in Fig. 4.11.

b) Give Examples of any known enzymes whose activity could be represented by

1) curve A and 2) curve B.

c) Why does the activity of enzyme C decrease between pH 8 and 9?

d) Why is the Introduction/15.html">Regulation of enzyme Activity via changes in pH important in vivo?

e) 1 ml of catalase solution was added to hydrogen peroxide solutions at various pH levels, and the time required to collect 10 ml of O₂ was recorded. The following results were obtained:

Plot these results on a graph and explain them.

Fig. 4.11. Effect of pH on the activity of three enzymes — A, B, and C.