Apoenzyme: What is it? Function, Types and Factors That Improve Your Activity

Enzymes are specialized proteins that act as catalysts to start complex chemical reactions.

All chemical reactions require some energy to start. The energy needed for the response to proceed is called activation energy.

Many of the most superficial chemical reactions require so little energy that they can occur at relatively low temperatures without any external influence.

When heat is added, the additional heat energy is often enough for many other reactions. More complex reactions require some further stimulus or catalyst to start.


Enzymes act as catalysts for chemical reactions by changing one or more of the reactants, called substrates, in a way that lowers the activation energy enough for the response to begin.

Some reactions will not occur without your specific enzymes. The enzyme is not necessary with some others, but it makes it more accessible.

Unlike reagents, enzymes are not consumed during the reaction. A holoenzyme is a complete, catalytically active form of the enzyme. It is made up of an apoenzyme together with its cofactor.


That protein part of the holoenzyme is called the apoenzyme, while the non-protein part is called the prosthetic group.

An apoenzyme is an inactive form of the enzyme that lacks the association of coenzymes and cofactors. Therefore, simple enzymes are also called apoenzymes. Thus, when a coenzyme or cofactor activates an enzyme, it becomes a haloenzyme.

Apoenzyme lacks biological activity and is catalytically inactive until bound by the appropriate cofactor.

Most cofactors are not covalently bound but are tightly bound. However, organic prosthetic groups such as an iron ion or vitamin can be covalently attached.

Examples of holoenzymes include DNA polymerase and RNA polymerase, containing multiple protein subunits.

Cofactors can be organic or inorganic, with the most common inorganic metal ions. Cofactors bind and are released from the active site of an enzyme, like a substrate.

The proper functioning of the body is because some cooperators can separate from their respective apoenzymes and perform specific functions.

The best-known example of this is nicotinamide adenine dinucleotide and flavin adenine dinucleotide, two coenzymes of dehydrogenase enzymes that, after hydrogen capture, are separated from the apoenzyme.

Its primary function is carried out in the metabolism of all living beings, with an essential role in the Krebs cycle.

Types of enzymes

Enzymes are primarily proteins in nature. Based on the composition, there are two types of enzymes:

  1. Proteoenzyme or simple enzymes: contain only amino acids and consist only of protein.
  2. Holoenzyme or conjugated enzymes: it is composed of proteins and a non-protein part, that is, of a simple enzyme and a cofactor, which is required for biological activity.


Enzymes work efficiently in association with various factors that enhance their activity.


They are small non-protein inorganic molecules that carry out chemical reactions that cannot be carried out by the standard of 20 amino acids.

Cofactors include metal ions like Fe, Cu, and Mg; they can also be an organic molecules like vitamin B.

Sometimes the enzyme alone is not enough to make a reaction work, and cofactors make the reaction work.

This molecule works by initiating or increasing the activity of an enzyme, inhibiting any process that inactivates an enzyme or reduces its effectiveness, whether competitively or non-competitively.


They are organic molecules that are not proteins and, for the most part, derived from vitamins that are soluble in water by phosphorylation. An example of a coenzyme includes thiamine pyrophosphates, flavin adenine dinucleotides, and biotins. Coenzymes are organic cofactors.

These organic molecules are part of the active sites of their protein enzymes. Since the coenzyme is part of the enzyme’s active site, the enzyme cannot work on the substrate without it.

Co-substrates are coenzymes that temporarily bind to the enzyme, will be released at some point, and will likely rejoin later.

A coenzyme that is tightly bound and is not released is called a prosthetic group.