Biochemical Engineering Fundamentals, Part 1 - Bailey J., Ollis D. 1989

Kinetics of Enzyme-Catalyzed Reactions
Other Factors Affecting Enzyme Activity

Before proceeding with the topic of this section, it is helpful to recall that the primary goal of this chapter is to describe the rates of enzyme-catalyzed reactions using mathematical expressions. Without the latter, we cannot design a Reactor or plan an experiment involving isolated Enzymes. Furthermore, when we begin studying Cell growth kinetics, we will find that various aspects of enzyme catalysis kinetics are applicable there as well. In this regard, Structure/19.html">The Importance of carefully studying the various factors influencing Enzymatic Catalysis, including quantifying the extent of their effects, becomes obvious.

Class="center">Table 3.8. Kinetic parameters of enzymatic reactions in the presence of various types of inhibitors; intercepts on the 1/v and 1/s axes

We already know that various chemical compounds, by binding to enzymes, can alter The rate of enzyme-catalyzed reactions, and we have a general understanding of how this occurs. The catalytic activity of enzymes is also influenced by many other factors that can alter the structure or Chemical Nature of the enzyme. These factors include:

1. pH

2. Temperature

3. Fluid forces (hydrodynamic forces, hydrostatic pressure, and surface tension)

4. Chemical agents (e.g., alcohol, urea, or hydrogen peroxide)

5. Irradiation (light, sound, ionizing radiation)

FIG. 3.22. Effect of the type of inhibition on various graphical representations of enzyme reaction kinetics. The subscript i denotes reaction parameters in the presence of an inhibitor. (From: Dixon M., Webb E., Enzymes, Vol. 2, p. 498, — Moscow: Mir, 1982.)

Sometimes, a decrease in catalytic activity caused, for example, by A change in pH, is reversible; in such cases, returning to the original conditions restores the enzyme's activity. In a sense, this situation is analogous to the case of reversible inhibition discussed earlier; small changes in one of the factors listed above, in fact, only slightly shift the equilibrium (or quasi-steady state) characteristic of a given enzymatic reaction. Generally, deviation from the conditions typical of the native enzyme's biological environment must be relatively small (or short-lived); otherwise, the probability of Enzyme inactivation increases. We will discuss many of the factors listed above in the next section on enzyme inactivation; here, the focus will be on the "reversible" effects of pH and temperature on the catalytic activity of enzymes.

It should be emphasized that the boundary between "reversible" and "irreversible" protein inactivation is not always clearly defined. For example, an enzyme subjected to brief heating may fully recover its activity upon cooling to its typical "operating" temperature. On the other hand, more prolonged heating at the same temperature, or an equally brief heat Treatment at a higher temperature, may result in only partial recovery of enzyme activity upon subsequent cooling. Such behavior of Proteins in general, and enzymes in particular, becomes understandable when considering the relationship between their Structure and function, The impact of Molecular Dynamics on protein function, and the possibility of disrupting certain weak bonds when environmental conditions change.