What are Enzymes?

Enzymes are important proteins whose function is to accelerate the speed of chemical reactions that occur in the body and that are necessary to maintain their biological activity, which they do by decreasing the activation energy.

Enzyme-catalyzed reactions occur at rates 1010 to 1014 times faster than non-catalyzed reactions. For example, urease accelerates the hydrolysis of urea in urine by a factor of 1014. This factor means that a catalyzed reaction that takes I second to occur could take a time of 3 million years without being catalyzed.

In every chemical reaction there is a transformation of an initial substance, called substrate (S), into a final substance or product (P), according to the following notation:

This transformation occurs through several stages. First, the enzyme “attracts” the substrate to its surface; then it “fixes” it in a certain position, and in this intermediate step an enzyme-substrate (ES) complex is formed. The substrate is then activated, so that its bonds are weakened, giving way to its transformation. Once the enzyme has completed the transformation, it quickly releases the reaction product to continue its work with other substrate molecules.

Structure of an enzyme

Like all proteins, enzymes are made up of a large number of amino acids, which have different functions. These include nonessential, structural, binding and catalytic amino acids.

  • Non-essential amino acids can be replaced, and in some cases eliminated without a significant loss in the function or conformation of an enzyme.
  • Structural amino acids are vital for the conformation of the enzyme, they “form its skeleton”.
  • Binding amino acids are involved in the association between the enzyme and the substrate.
  • Catalytic amino acids actively participate in the transformation of the substrate.

The “structure” of an enzyme can be explained in terms of the residues of these four types of amino acids. Obviously, the structural, binding and catalytic residues can be considered essential and any modification of these residues decreases the enzymatic activity. In fact, if the residue is particularly crucial, as in the case of a key binding residue or any catalytic residue, a total loss of activity results.

The site where the set of binding and catalytic amino acids is located is called the active center of the enzyme, a strategic location where, by means of intermolecular bonds, the enzyme “attracts” the substrate in such an orientation that they fit together correctly, like the pieces in a jigsaw puzzle.

Regulation of enzyme activity

As with any protein, the activity of an enzyme depends on factors such as temperature, degree of acidity or pH, salt solutions, solvents, activators and inhibitors.

Temperature factor

If the temperature of an enzymatic reaction is increased, the kinetic energy of the particles increases. The increase in the mobility of these molecules produces an increase in the number of collisions, increasing the speed of the transformation. If the temperature continues to increase, some intermolecular bonds responsible for the conformation of the enzyme begin to break and, thus, its activity begins to gradually decrease. If the temperature is too high, the enzyme is denatured and loses its catalytic properties completely.

pH factor

When the pH of the medium varies, changes occur in the ionization state of some ionizable groups of an enzyme, affecting its three-dimensional structure and, therefore, its biological activity. In addition, the change in the ionization state of chemical groups located in the active site can alter the recognition of the substrate or the reactivity of the amino acids associated with the enzyme’s active site. All enzymes have two pH threshold values between which they are effective. If these values are exceeded, the enzyme is denatured and ceases to act.

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