Enzymes are a type of protein present in all living things. They are secreted by the source and are biological catalysts, increasing the rate of chemical reactions without undergoing any permanent change themselves. They continue to work as long as the “substrate” is present.

Enzymes are biomolecules (usually proteins) that dramatically accelerate the speed of almost all chemical reactions occurring within a cell. They are vital to life and provide a wide range of important functions in the body, such as helping digestion and metabolism. Industrial enzymes help break down macromolecules into smaller pieces that are more easily absorbed by the body. Other enzymes help to bind the two molecules together to create a new molecule. Enzymes are highly selective catalysts, meaning that each enzyme only accelerates a particular reaction. The molecule with which the enzyme is associated is called a substrate. The substrate binds to a region on the enzyme called the active site.

Enzymes are proteins that catalyse biochemical reactions and exist within all living organisms. Responsible for regulation of biological functions such as signal transduction and metabolism, each enzyme is highly specific for the type of reaction it catalyses.

Enzymes are substances found in biological systems and are catalysts for specific biochemical processes. Despite the early discovery of enzymes, German chemist Eduard discovered important evidence of their importance in the life system in 1897, showing that filtered cell-free fluids from crushed yeast cells convert sugar into carbon dioxide. Since then, more than 1,000 enzymes for research have been identified, each specific for a specific chemical reaction that occurs in the living system. More than 100 of them are isolated in relatively pure form, including many crystallization enzymes.

One of the basic tasks of proteins is to act as an enzyme catalyst that increases the rate of almost all chemical reactions in a cell. Although RNA can catalyze some reactions, most biological reactions are catalyzed by proteins. In the absence of enzymatic catalysis, most biochemical reactions are so slow that they do not occur under mild and temperature conditions that are compatible with life. Enzymes accelerate this reaction by more than a million times, so if it is catalyzed by appropriate enzymes, the reaction that takes years without catalysis can occur in a matter of seconds. Cells contain thousands of different enzymes whose activity determines many of the possible chemical reactions that actually occur within the cell.

Enzyme activity can also be regulated by their interaction with other proteins and by covalent enzyme modification, such as the addition of a phosphate group to a serine, threonine or tyrosine residue. Phosphorylation is a particularly common mechanism for modulating enzyme activity; the addition of a phosphate group can stimulate or inhibit the activity of many different enzymes (Figure 2.30). For example, muscle cells respond to adrenaline (epinephrine) by breaking down glycogen into glucose, thereby providing a source of energy that increases muscle activity. The breakdown of glycogen is catalyzed by glycogen phosphorylase, which is activated by phosphorylation in response to binding of adrenaline to receptors on the surface of muscle cells. Protein phosphorylation plays an important role in controlling metabolic reactions as well as many other cellular functions, including cell growth and differentiation.

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