Biochemistry

It was established that enzymes of animal origin show the highest activity at a temperature of 37-40 °C, and plant - at 50 and 60 ° C. This temperature is called the temperature optimum (Fig. 3.6). However, there are exceptions, for example, catalase is most active at a temperature of 0-10 °C. Heating to a temperature of 50-60 °C weakens the effect of enzymes of animal origin. At a temperature of 70 °C and above, most of them completely lose their activity. At low temperatures (hypothermia), the activity of enzymes decreases, but does not disappear. It has been established that in the refrigeration chambers in frozen meat there is a slow protein breakdown under the action of proteolytic enzymes. When the temperature optimum is created for the enzymes, they become active again. An example is the hibernation of animals. This ability of enzymes is used in surgery, cryobiology. The activity of enzymes is influenced by a certain concentration of hydrogen ions - the pH of the medium (Fig. 3.4). For each enzyme, there is a certain narrow limit of the pH of the medium, which is optimal for the realization of its maximum activity. Deviation of pH from the optimal value leads to a decrease in the activity of the enzyme or even to its irreversible inactivation. The optimum pH is 1.5-2.5 for pepsin, 8.0-8.5 trypsin, saliva amylase 6.8-7.4, and arginase 9.7. Changes in the catalytic effect of enzymes at various pH values of the medium can be associated with changes in the configuration of the unique structure of the molecule — its active center. The rate of enzymatic reactions depends not only on the temperature and pH of the medium, but also on the concentration of the enzyme and substrate, the presence of activators and paralyzers. Figure 3.5 shows the dependence of the enzymatic reaction on the concentration of the enzyme. The rate of action of the enzyme is determined by the concentration of the resulting enzyme-substrate complex. The maximum reaction rate is achieved when the concentration of the substrate is sufficient to bind the entire amount of the enzyme to the enzyme-substrate complex. Figure 3.4 - Enzymes activity dependency from PH Figure 3.5 - Enzymes activity dependency from their concentration 86