Basics of Enzyme Kinetics
The study of how fast chemical reactions proceed under the action of biocatalysts is known as enzyme kinetics. This branch of enzymology analyzes the dependence of the reaction rate on two key groups of factors:
- The chemical nature of the reacting substances (substrates).
- Environmental conditions (temperature, acidity, and other parameters).
How is Reaction Rate Expressed?
To assess catalytic activity, specialists always focus on the reaction rate. In biochemistry, it is defined as the change in the amount of molecules over a strictly defined period of time.
This change can be recorded in two equivalent ways:
- By assessing the decrease in the amount of the starting material (substrate).
- By measuring the increase in the amount of the formed product.
This rate serves as the universal measure of catalytic capacity, commonly referred to simply as enzyme activity.
International Unit of Activity (IU)
Since counting absolute numbers of molecules is impractical, medical and pharmaceutical practice uses standardized conventional units. The main one is the International Unit (IU or U).
One IU is precisely the amount of enzyme required to catalyze the conversion of 1 µmol of substrate per 1 minute.
Crucial rule: measurements are always performed under standard conditions that must be optimal for the specific enzyme. Typically, this is a temperature of $37^\circ$C and an ideal pH level for the given protein.
Specific Activity and Preparation Purity
In laboratory settings, enzymes are often found in solution alongside many other tissue proteins. To determine how pure an isolated preparation is, specific activity (Sp. Act.) is calculated.
This parameter reflects the number of units of enzymatic activity per 1 milligram of total protein in the sample.
Calculation Formula: Sp. Act. = Amount of converted substrate (in µmol) / [Time (in min) × Amount of protein (in mg)]
Clinical Significance: The parameter directly indicates the degree of enzyme purification. The logic is simple: the fewer extraneous contaminating proteins in your sample, the higher the specific activity value will be.