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General Characteristics and Properties of Enzymes

Enzyma

For medical students2 min readUpdated 2026-10-10

Enzymes are biological catalysts of protein nature that provide a manifold acceleration of chemical reactions in living cells. They function by lowering the activation energy and operate under strictly defined, mild physiological conditions.

NatureCan be simple proteins or complex proteins (holoenzymes)

SpeedAccelerate reactions by a factor of 10^8 to 10^14 compared to uncatalyzed reactions

EfficiencyA single molecule transforms from 100 to 1,000 substrate molecules per second

ConditionsOptimal operating range: 37–38 °C at normal atmospheric pressure

Fundamental Similarities with Chemical Catalysis

Enzymes obey the general laws of catalysis and share several fundamental similarities with non-biological (chemical) catalysts. These basic principles determine the very possibility of reactions occurring in living systems:

Energetic Feasibility. Enzymes are capable of accelerating exclusively those reactions that are thermodynamically favorable.
Constancy of Energy. During an enzymatic reaction, the total energy of the chemical system remains unchanged.
Conservation of the Catalyst. Like any classical catalyst, enzymes are not consumed in the reaction, returning to their original state after the product is released.

Specific Properties of Biological Catalysts

Despite similarities with chemical analogs, enzymes possess three unique features due to their protein nature.

Specificity of Action

Enzymes act with extreme selectivity. This feature is directly related to the presence of the active site—a specialized region on the surface of the protein molecule. It is the active site that interacts with a strictly defined ligand known in enzymology as the substrate. Specificity can manifest in various forms, including absolute specificity, relative specificity, and stereospecificity.

Enormous Catalytic Efficiency

Reaction rates under the action of enzymes are incredibly high. Enzymes can accelerate chemical processes by $10^8$ to $10^{14}$ times compared to reactions proceeding without catalysts. The turnover number is such that a single enzyme molecule manages to transform 100 to 1,000 substrate molecules per second.

Conformational Labile Nature

An enzyme's catalytic efficiency depends directly on the spatial conformation of its protein molecule (primarily the structure of the active site). The enzyme molecule is flexible and mobile. Various substances within the cell can cause the breaking or formation of weak chemical bonds within the enzyme, leading to minor conformational changes that increase or decrease catalytic activity. Thus, enzymes are capable of regulation (e.g., allosteric regulation or covalent modification).

Optimal Physiological Conditions

One of the most important differences between enzymes and non-biological catalysts is their ability to work under mild physiological conditions. While industrial chemical catalysis often requires extremely high temperatures, colossal pressure, or harsh pH extremes, enzymes perform their tasks within the delicate environment of a living cell:

Temperature: optimal values lie within a narrow range of 37–38 °C.
Pressure: reactions occur at normal atmospheric pressure.
Acidity (pH): for the vast majority of tissues, the optimal pH is within 6.9–7.7.

Mnemonic

The three pillars of enzyme properties can be easily remembered by the acronym SEC: Specificity, Efficiency (catalytic), and Conformational lability.

Frequently asked questions

What types of enzyme specificity are distinguished?

Several types of substrate and reaction specificity are distinguished:

Absolute substrate specificity — the active site is complementary to only one substrate.
Group (relative) specificity — the enzyme catalyzes a similar type of reaction with a group of structurally similar substrates.
Stereospecificity — the enzyme exhibits absolute specificity for only one of the stereoisomers of a substrate.
Reaction specificity — the ability to catalyze only one type of reaction.

What structural components make up complex enzymes (holoenzymes)?

Complex enzymes (holoenzymes) consist of two main structural components: a protein part and a non-protein part.

Apoenzyme — the protein part of the enzyme, which lacks catalytic activity in the absence of the coenzyme.
Cofactor — the non-protein component (metal ions, coenzymes, or prosthetic groups) necessary for enzyme activity.

The complete catalytically active complex of an apoenzyme with its cofactor is called a holoenzyme.

What functional zones (regions) are distinguished in the structure of an enzyme's active site?

Two main functional zones formed by amino acid residues are distinguished in the active site of an enzyme:

Binding site (sorption or anchor site) — ensures complementary binding of the substrate.
Catalytic site — carries out the chemical transformation of the substrate.

The active site is formed by amino acid side chains; amino acids forming the active site may be far apart in the polypeptide chain but are brought close together in the tertiary structure of the protein.

Through which molecular mechanisms do enzymes lower the activation energy of a reaction?

Enzymes lower activation energy through several molecular processes during the formation of the enzyme-substrate complex:

Proximity and orientation of the substrate within the enzyme's active site.
Induced fit — a conformational change in both the substrate and the enzyme's active site.
Destabilization of bonds in the substrate upon formation of the unstable enzyme-product complex.

As a result of these steps, the height of the energy barrier is lowered, which increases the proportion of reactive molecules.

What is the mechanism of allosteric regulation of enzyme activity?

The mechanism of allosteric regulation involves the non-covalent binding of an effector to the allosteric (regulatory) site of an enzyme. This interaction induces cooperative conformational changes throughout the oligomeric protein structure. As a result, the conformation of the active site and its affinity for the substrate change. Binding of an activator increases substrate affinity and reaction rate, whereas binding of an inhibitor decreases affinity and suppresses enzyme function.

How is enzyme activity regulated via covalent modification?

Regulation of enzyme activity by covalent modification occurs, in particular, through phosphorylation-dephosphorylation. Phosphorylation-dephosphorylation is one of the primary mechanisms regulating enzyme activity. It belongs to covalent modification and is a rapid and widespread method of chemical modification of enzymes. The essence of the mechanism lies in the reversible addition or removal of a phosphate group, which alters the enzyme's activity.

Does the total energy of a chemical system change in the presence of an enzyme?

No, enzymes keep the total energy of the chemical system constant; they merely lower the activation energy, accelerating the attainment of equilibrium.

What accounts for the high specificity of enzymes?

Specificity is provided by a special region of the protein molecule called the active site, whose geometric and chemical structure is uniquely complementary to a specific substrate.

Are enzymes consumed during catalysis?

No, like any other catalysts, enzymes are not consumed during a chemical reaction and can participate in it repeatedly.

Go deeper

Structure and function of the enzyme active site
Types of specificity: absolute, relative, and stereospecificity
Differences between simple and complex enzymes (structure of holoenzymes)
Mechanisms of activation energy reduction
Types of enzyme activity regulation (allosteric regulation, covalent modification)