BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 7. ENZYMOLOGY

7.5. Fundamentals of Enzyme Reaction Kinetics

Enzyme kinetics is a branch of enzymology that investigates how the rates of enzyme-catalyzed Chemical Reactions depend on the Chemical Nature of the reactants and various environmental factors.

To measure the catalytic activity of Enzymes, parameters such as reaction rate or enzyme activity are used. The rate of an enzymatic reaction is determined by The change in the number of substrate or product molecules per unit of time. The reaction rate serves as a measure of the enzyme's catalytic activity and is referred to as enzyme activity. Mathematically, the rate of an enzymatic reaction is expressed as the change in Substrate Concentration (decrease) or product concentration (increase) per unit of time:

Class="center">

During the initial stage [t₀ - t₁], the reaction rate is directly proportional to time, exhibiting a linear relationship. Graphically, the change in the rate of an enzymatic reaction is determined by the tangent of the angle of the tangent line to the reaction progress curve. The larger the slope angle, the greater the change in the reaction rate (Fig. 7.15).

In enzyme-catalyzed reactions 1 and 2, the initial reaction rate catalyzed by enzyme 1 is lower than that catalyzed by enzyme 2. This is because the slope of the tangent line to the reaction progress curve drawn from point "0" is steeper for the second enzyme, both in terms of product accumulation (A) and substrate depletion (B).

Fig. 7.15. Dependence of product accumulation (A) and substrate depletion (B) on the reaction time for reactions 1 and 2

After a certain period, the rate of the enzymatic reaction decreases under experimental conditions, as indicated by the changing slope of the tangent line at time t. This decline in reaction rate can be attributed to several factors: a decrease in substrate concentration, an increase in product concentration (which may exert an inhibitory effect), changes in solution pH, Enzyme inactivation, etc.

At the [t₁ - t_x] stage, the reaction rate changes non-linearly with time. Therefore, to accurately determine the rate of an enzymatic reaction, researchers typically analyze the rate changes during the initial stage [t₀ — t₁], where a linear change in product (or substrate) concentration is observed.

The rate of an enzymatic reaction depends on A number of factors, such as the amount and activity of enzymes, substrate concentration, ambient Temperature, solution pH, and the presence of regulatory molecules (activators and inhibitors). Let us examine METABOLISM/18.html">The Influence of these factors on the Rate of Enzymatic reactions.