Holoenzyme: properties, functions and examples (2023)

AHoloenzymeIt is an enzyme formed from a part of the protein called an apoenzyme in combination with a non-protein molecule called a cofactor. Neither the apoenzyme nor the cofactor are active when cleaved; that is, in order for them to work, they must be paired.

Thus, holoenzymes are enzymes that combine and are therefore catalytically active. Enzymes are a type of biomolecules whose main function is to increase the speed of cellular reactions. Some enzymes need the help of other molecules called cofactors.

Holoenzyme: properties, functions and examples (1)Apoenzima + Cofactor = Holoenzima

The cofactors are complemented by apoenzymes, forming an active holoenzyme that performs the catalysis. Those enzymes that require a specific cofactor are called conjugated enzymes. These consist of two main components: the cofactor, which can be a metal ion (inorganic) or an organic molecule; the apoenzyme, a part of the protein.


(Video) Enzymes Cofactors | Coenzyme vs prosthetic group | Apoenzyme Vs holoenzyme

  • 1 properties
    • 1.1 Formed by apoenzymes and cofactors
    • 1.2 Allow a variety of cofactors
    • 1.3 Temporary or Permanent Membership
  • 2 functions
  • 3 The 11 examples of common holoenzymes
    • 3.1 1-RNA polymerase
    • 3.2 2-DNA polymerase
    • 3.3 3- Carboanidrasa
    • 3.4 4-Hemoglobin
    • 3.5 5- Cytochrome oxidase
    • 3.6 6- Pyruvatekinase
    • 3.7 7- Pyruvatcarboxylase
    • 3.8 8-Acetyl-CoA-Carboxylase
    • 3,9 9-Monoaminoxidasa
    • 3.10 10- Lactatdesidrogenasa
    • 3.11 11- Catalase
  • 4 references


Made up of apoenzymes and cofactors.

The apoenzymes are the protein part of the complex and the cofactors can be ions or organic molecules.

They allow for a variety of cofactors.

There are different types of cofactors that help form holoenzymes. Some examples are common coenzymes and vitamins, for example: vitamin B, FAD, NAD+, vitamin C, and coenzyme A. Some cofactors with metal ions, for example, copper, iron, zinc, calcium, and magnesium, among others. Another class of cofactors are the so-called prosthetic groups.

Temporary or permanent union

Cofactors can be linked to apoenzymes to varying degrees. In some cases the bond is weak and temporary, while in other cases it is so strong that it is permanent.

In cases where the association is transient, when the cofactor of the holoenzyme is removed, it reverts to being an apoenzyme and is no longer active.


The holoenzyme is an enzyme prepared to perform its catalytic function; that is, to speed up certain chemical reactions generated in different areas.

The functions may vary depending on the specific action of the holoenzyme. One of the most important is DNA polymerase, whose job is to make sure that DNA is copied correctly.

The 11 Examples of Common Holoenzymes

1- RNA polymerase

RNA polymerase is a holoenzyme that catalyzes the RNA synthesis reaction. This holoenzyme is required to build RNA strands from DNA template strands, which act as templates during the transcription process.

Its function is to add ribonucleotides to the 3' end of a growing RNA molecule. In prokaryotes, the RNA polymerase apoenzyme requires a cofactor called sigma 70.

(Video) Apoenzyme, Holoenzyme, Coenzyme & Cofactor

2- DNA polymerase

DNA polymerase is also a holoenzyme that catalyzes the DNA polymerization reaction. This enzyme plays a very important role for cells since it is in charge of duplicating genetic information.

DNA polymerase requires a positively charged ion, usually magnesium, to perform its function.

There are several types of DNA polymerases: DNA polymerase III is a holoenzyme with two core enzymes (Pol III), each composed of three subunits (α, ɛ, and θ), a sliding clamp with two beta subunits, and a cargo complex for unite with several subunits (δ, τ, γ, ψ and χ).

3- carboanidrasa

Carbonic anhydrase, also known as carbonate dehydratase, belongs to a family of holoenzymes that catalyze the rapid conversion of carbon dioxide (CO2) and water (H2O) into bicarbonate (H2CO3) and protons (H+).

The enzyme requires a zinc ion (Zn+2) as a cofactor to perform its function. The reaction catalyzed by carbonic anhydrase is reversible, so its activity is considered important, since it helps to maintain the acid-base balance between blood and tissues.

4- Hemoglobin

Hemoglobin is a very important holoenzyme for the transport of gases in animal tissues. This protein, present in red blood cells, contains iron (Fe+2) and has the function of transporting oxygen from the lungs to other areas of the body.

The molecular structure of hemoglobin is a tetramer, which means that it is made up of 4 polypeptide chains, or subunits.

Each subunit of this holoenzyme contains a heme group, and each heme group contains an iron atom that can bind oxygen molecules. The heme group of hemoglobin is its prosthetic group, necessary for its catalytic function.

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5- Cytochrome oxidase

Cytochrome oxidase is an enzyme involved in the energy production processes that occur in the mitochondria of almost all living things.

It is a complex holoenzyme that requires the cooperation of certain cofactors, iron and copper ions, to catalyze the electron transfer reaction and the production of ATP.

6- Pyruvatekinase

Pyruvate kinase is another important holoenzyme for all cells, since it is involved in one of the universal metabolic pathways: glycolysis.

Its function is to catalyze the transfer of a phosphate group from a molecule called phosphoenolpyruvate to another molecule called adenosine diphosphate to form ATP and pyruvate.

7- Pyruvatcarboxylase

Another important example is pyruvate carboxylase, a holoenzyme that catalyzes the transfer of a carboxyl group to a pyruvate molecule. This is how pyruvate is converted to oxaloacetate, an important intermediate in metabolism.

To be functionally active, the pyruvate carboxylase apoenzyme requires a cofactor called biotin.

8- Acetyl-CoA-Carboxylase

Acetyl-CoA carboxylase is a holoenzyme whose cofactor, as its name suggests, is coenzyme A.

When apoenzyme and coenzyme A couple, the holoenzyme is catalytically active to carry out its function: to transfer a carboxyl group to acetyl-CoA to convert it to malonyl-coenzyme A (malonyl-CoA).

(Video) 2 : Coenzymes: Properties/ Examples | Enzymes| Biochemistry | @NJOYBiochemistry

Acetyl-CoA plays an important role in animal and plant cells.

9- Monoaminoxidasa

This is an important holoenzyme in the nervous system whose function is to promote the breakdown of certain neurotransmitters.

For monoamine oxidase to be catalytically active, it must be covalently linked to its cofactor, flavin adenine dinucleotide (FAD).

10-lactate dehydrogenase

Lactate dehydrogenase is an important holoenzyme for all living things, especially in energy-intensive tissues such as the heart, brain, liver, skeletal muscles, lungs, and others.

This enzyme requires the presence of its cofactor, nicotinamide adenine dinucleotide (NAD), to catalyze the conversion reaction from pyruvate to lactate.

11- Catalase

Catalase is an important holoenzyme in the prevention of cell toxicity. Its function is to break down hydrogen peroxide, a product of cell metabolism, into oxygen and water.

The catalase apoenzyme requires two cofactors to activate: a manganese ion and a HEMO prosthetic group, similar to that of hemoglobin.


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  7. Gupta, V. & Bamezai, R.N.K. (2010). Human Pyruvatkinase M2: A multifunctional protein.protein science,19(11), 2031-2044.
  8. Jitrapakdee, S., St. Maurice, M., Rayment, I., Cleland, W.W., Wallace, J.C. y Attwood, P.V. (2008). Struktur, Mechanismus und Regulation der Pyruvatcarboxylase.Biochemical Magazine,413(3), 369-387.
  9. Muirhead, H. (1990). Isoenzima der Pyruvatkinase.Transactions of the Biochemical Society,18, 193-196.
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  11. Weep, CT (2016). Structure and function of carbonic anhydrases.Biochemical Magazine,473(14), 2023-2032.
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(Video) What are enzymes? Cofactor, coenzyme, prosthetic group, apoenzyme, holoenzyme.


What are the properties of holoenzyme? ›

Holoenzyme- An apoenzyme together with its cofactor. A holoenzyme is complete and catalytically active. Most cofactors are not covalently bound but instead are tightly bound. However, organic prosthetic groups such as an iron ion or a vitamin can be covalently bound.

What is holoenzyme and its function? ›

Holoenzyme is a complete, functional enzyme, which is catalytically active. Holoenzyme consists of an apoenzyme together with its cofactors. Holoenzyme contains all the subunits required for the functioning of an enzyme, e.g. DNA polymerase III, RNA polymerase. Holoenzyme = Apoenzyme + Cofactor.

What are holoenzymes examples? ›

Some examples of holoenzymes are DNA polymerase and RNA polymerase. These enzymes consist of multi-protein subunits. Thus, they are complete and complex.

What are the examples of holoenzyme and apoenzyme? ›

Example: DNA polymerase and RNA polymerase are two holoenzymes which require magnesium ions to become active and initiate polymerization. It consists of the protein part of the enzyme. Example: Catalytic components of DNA polymerase enzyme are called as apoenzymes.

What is the function of holoenzyme in transcription? ›

Initiation of transcription is a primary means for controlling gene expression. In bacteria, the RNA polymerase (RNAP) holoenzyme binds and unwinds promoter DNA, forming the transcription bubble of the open promoter complex (RPo).

What are the components of a holoenzyme? ›

The holoenzyme consists of the following two components: (1) the core enzyme and (2) the sigma factor. The holoenzyme may be symbolized as α2 β β' σ. !

Is holoenzyme a functional unit? ›

Correct option D All of theseExplanation:The functional unit of an enzyme is referred to as a holoenzyme. It is often made up of an apoenzyme the protein part and a coenzyme the non-protein part.

What three components make holoenzyme? ›

The holoenzyme contains at least seven different subunits. Three of these, alpha, epsilon and theta, compose the catalytic core. Apparently alpha is the catalytic subunit and the product of the dnaE gene.

What is the function of apoenzyme? ›

Apoenzyme is the protein part of an enzyme. The non-protein part cofactor together with the protein part apoenzyme forms a holoenzyme. Apoenzymes are important for enzymatic activity since they are responsible for the specificity of enzymes to their substrates.

What is a holoenzyme quizlet? ›

Holoenzyme definition. an enzyme complete with its apoenzyme and cofactors. Apoenzyme definition. the protein part of an enzyme, as opposed to the nonprotein or inorganic cofactors.

What is holoenzyme classification? ›

(ii) Holoenzyme or Conjugate enzyme:

The cofactors are of 3 types: Co-enzymes, Prosthetic groups and inorganic ions.

Where are holoenzymes found? ›

CaMKII holoenzymes contain 12 nearly identical molecules of an enzyme called CaM kinase II (CaMKII), arranged into two hexagonal rings, and they are found at the synapses that connect nerve cells with each other.

Is DNA example of holoenzyme? ›

DNA polymerase and RNA polymerase are two examples of holoenzymes. Multi-protein subunits make up these enzymes. As a result, they are both complete and complex. A biological reaction can only be catalysed by holoenzymes.

What is an example for apoenzyme? ›

(b) Example of apoenzyme is apo glucose oxidase. (c) Examples of coenzymes are the B vitamins and S-adenosylmethionine.

What is the difference between an apoenzyme and a holoenzyme? ›

Answer: Apoenzyme and holoenzyme are two enzyme states. The primary distinction between apoenzyme and holoenzyme is that apoenzyme is the enzyme's catalytically inactive protein component, whereas holoenzyme is the enzyme's catalytically active form, consisting of the apoenzyme and the cofactor.

What is the holoenzyme for eukaryotic transcription? ›

In eukaryotes, holoenzymes are large preassembled complexes containing RNA polymerases and variable sets of general transcription initiation factors and cofactors that are important for the regulation of gene expression.

What is a holoenzyme in genetics? ›

The holoenzyme is a multiprotein complex containing the multimeric RNA polymerase II protein that transcribes pro- tein coding genes, most of the general tran- scription factors required for the poly- merase to locate eukaryotic promoters and initiate transcription, and a newly discov- ered multimeric protein complex ...

What is a holoenzyme in transcription prokaryotic? ›

Without σ, the core enzyme would transcribe from random sites and would produce mRNA molecules that specified protein gibberish. The polymerase comprised of all five subunits is called the holoenzyme (a holoenzyme is a biochemically active compound comprised of an enzyme and its coenzyme).

Which of the following correctly describes a holoenzyme? ›

Holoenzyme is the active form of the enzyme. It is made of 2 components called the apoenzyme and coenzyme. A cofactor can also be called a coenzyme if it is an organic molecule.

What is the protein part of holoenzyme called? ›

The protein part of the holoenzyme is known as the apoenzyme, which is inactive.

What is the holoenzyme composed of quizlet? ›

A holoenzyme is composed of apoenzyme and cofactor/coenzyme. A conjugated enzyme consists of a protein component called the cofactor and one or more activators called apoenzymes. if an enzyme is rendered inactive by temperature, pH or chemicals, it has been denatured.

What is an example of a functional unit? ›

A functional unit is a quantified description of the performance of the product systems, for use as a reference unit. Example: Lighting 10 square metres with 3000 lux for 50000 hours with daylight spectrum at 5600 K. the performance described by the functional unit.

What is the function of functional unit? ›

A functional unit describes a quantity of a product or product system on the basis of the performance it delivers in its end-use application. Functional units are foundational to LCA and TEA, as they enable objective comparisons across different products or systems that serve the same final function.

How is holoenzyme formed? ›

In the presence of polymerase, holoenzyme assembly involved the recruitment of the polymerase to the gp45−gp44/62−DNA complex mediated by the chaperoning activity of gp44/62. This transient multiprotein complex then decomposed through an ATP hydrolysis−dependent exit of gp44/62 leaving the holoenzyme on DNA.

What is holoenzyme apoenzyme and coenzyme? ›

Holoenzyme is a complete and catalytically active enzyme consisting of protein part (apoenzyme) together with its bound coenzyme and/or metal ions. • A coenzyme or metal ion (non-protein part) that is very tightly or even covalently bound to the enzyme protein is called a prosthetic group.

Which part of holoenzyme is called as apoenzyme? ›

Apoenzyme is a protein portion, which combines with a cofactor, i. e. either coenzyme, metal ion activatior or prostheic group and is collectively called an active holoenzyme.

What are the properties and characteristics of enzyme? ›

They have high catalytic power and can quickly catalyze a chemical reaction with a tiny quantity. They accelerate reactions while remaining unaltered during the process. Temperature, pH, and inhibitors can all have an impact on enzyme performance and function.

What are the properties of cofactor? ›

Cofactor. The cofactor of a minor of A:n#n is equal to the product of (i) the determinant of the submatrix consisting of all the rows and columns that are not in the minor and (ii) -1 raised to the power of the sum of all the row and column indices that are in the minor.

What are the 7 main properties of enzymes? ›

  • Enzymes are complex macromolecules with high molecular weight.
  • They catalyze biochemical reactions in a cell. ...
  • Enzymes do not start a reaction. ...
  • Enzymes affect the rate of biochemical reaction and not the direction. ...
  • Enzymes are specific in action.
  • Enzymatic activity decreases with increase in temperature.

Is Holoenzyme an active enzyme? ›

The fully active enzyme is called a holoenzyme, and it is composed of a protein portion (apoenzyme) and cofactor.

What are the 4 main characteristics of enzymes? ›

Main characteristics of an enzyme:
  • It is a protein and therefore, gets destroyed by heating.
  • It acts only on one kind of substance called the substrate. ...
  • It acts as a catalyst, so it can be used again and again.
  • It only affects the rate of a chemical reaction.

What is holoenzyme also known as? ›

The holoenzyme is a conjugate enzyme which consists of two parts non-protein parts i.e., apoenzymes and protein part i.e., cofactor. It is also called as a complete enzyme.

What are 5 characteristics of enzymes? ›

Characteristics of an Enzyme :
  • Speed up chemical reactions.
  • They are required in minute amounts.
  • They are highly specific in their action.
  • They are affected by temperature.
  • They are affected by pH.
  • Some catalyze reversible reactions.
  • Some require coenzymes.
  • They are inhibited by inhibitors.

How many properties do enzymes have? ›

Ans-The four main features of an enzyme are as follows: they have tremendous catalytic power and can easily catalyse a chemical reaction when only a small amount is present. They have the ability to accelerate reactions while remaining unchanged throughout the entire reaction.

What are cofactors and their functions? ›

Cofactors can be metals or small organic molecules, and their primary function is to assist in enzyme activity. They are able to assist in performing certain, necessary, reactions the enzyme cannot perform alone. They are divided into coenzymes and prosthetic groups.

What are the 3 types of cofactors give examples? ›

Cofactors can be divided into two major groups: organic cofactors, such as flavin or heme; and inorganic cofactors, such as the metal ions Mg2+, Cu+, Mn2+ and iron–sulfur clusters. Organic cofactors are sometimes further divided into coenzymes and prosthetic groups.

What is the function of cofactor in enzyme? ›

Functions of Enzyme Cofactors

Cofactors usually have the function of contributing chemical groups or qualities that are absent from other chemical groups. For example, the cofactor ATP can transfer energy, which it uses to conduct chemical reactions like enzyme activities and protein transportation.


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