Enzymes are biological catalysts, most of the enzymes are proteins and like other proteins enzymes also have secondary and tertiary structure. Enzymes are highly specific in binding to substrates and the substrate binds to the enzyme at active sites, which are the crevices or pockets formed by the folding of protein chains in its tertiary structure. Enzymes (E) bind to the substrate (S) and form a transient ES complex. Enzymes lower the activation energy to reach the transition state.
The enzyme activity is highly dependent on the conditions that affect its tertiary structure. Enzyme activity is affected by factors such as temperature, pH, the concentration of substrates, presence of inhibitors, allosteric regulators, etc.
Temperature and pH
Enzymes work optimally between a certain range of pH and temperature. Enzymes get denatured at extreme temperatures and pH and lose their ability to bind to substrates. Each enzyme has a specific optimum temperature and pH at which it shows the maximum activity, e.g. optimum pH for pepsin is 1.8, whereas for salivary amylase it is 6.8. There is a decline in its activity both above and below the optimum value.
Concentration of Substrate
The velocity of the reaction increases with an increase in the concentration of substrate initially. It reaches the peak value (Vmax) and there is no further increase after that. At this point, all the active sites of the enzyme get saturated with the substrate and there are no sites left for binding with the substrate.
Enzyme activity is also affected by regulators such as competitive inhibitor. The competitive inhibitor has structural similarity with the substrate molecule and competes for the binding site present on enzymes, e.g. malonate inhibits succinate dehydrogenase due to structural similarities with succinate, which is the substrate for succinate dehydrogenase enzyme.
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