Enzymes are large biomolecules produced by cells, and their main component is protein. Factors that affect protein structure also influence enzyme activity.
Increasing temperature intensifies the random motion of molecules. Enzymes have a higher chance of capturing substrates and the substrates gain higher activation energy. For every 10°C increase in temperature, the rate of enzyme-catalyzed reactions usually increases by 50% to 100%. However, excessively high temperatures breaks the chemical bonds to alter the enzyme's conformation. Initially, as temperature increases, enzyme activity increases. The activity of enzymes is maximal at the optimal temperature. Then, the temperature increases will inhibit enzyme activity until the enzyme becomes completely inactive.
The optimal temperature of an enzyme is dependent on its type, pH value, ion concentration, and duration of work, and there is no fixed value. Typically, the optimal temperature for animal enzymes is between 35 to 40°C, while for plant enzymes, it is between 40 to 50°C. Some thermophilic microbial enzymes can even have an optimal temperature as high as 70°C.
Enzymes have an optimal pH value at which their activity is highest. Deviating from this optimal pH value can lead to decreased or complete loss of enzyme activity. When the pH value deviates only slightly from the optimal point, the enzyme's activity decreases but doesn't completely cease. The protein adsorbs more positive or negative charges, and some groups move closer or farther apart. Slight changes of enzyme active site mildly impede the binding and breakdown of the substrate to the enzyme. Extreme pH values (too high or too low) can redistribute hydrogen bonds and ionic bonds and even disrupt peptide bonds, resulting in a drastic change in the enzyme structure and complete loss of catalytic activity.
Similar to the optimal temperature of enzymes, the optimal pH value is influenced by various factors and does not have a fixed value. For example, pepsin, an enzyme in the stomach, is most active at pH 1.5 to 2, while trypsin functions optimally at pH 7 to 8.
If there is a limited amount of substrate, many enzymes remain idle. The increase in substrate puts the free enzyme to use, so the reaction rate rises. However, once all the enzymes are working, the substrate concentration increase does not change the reaction rate.