The difference between cofactor and coenzyme is mainly due to the following factors:
Chemical nature: Cofactors constitutes a large group of helper molecules that can be inorganic and organic, while cofactors are simply the small, organic molecules.
Function: Coenzymes significantly acts as a carrier material to convert the inactive protein (Apoenzyme) into the active form (Holoenzyme). In contrast, cofactors only fasten the enzymatic reaction inside a cell.
Both cofactor and coenzyme are important terms to study the chemical and physical properties of an enzyme. It is important to note that the cofactors or coenzymes only attach to the types of conjugated enzymes that also contain a non-protein region. Hence, the simple enzymes that entirely contains amino acids do not require any additional carriers to show its catalytic activity.
Content: Cofactor Vs Coenzyme
|Alternative names||Helper molecules or accessory molecules||Co-substrate or secondary substrate|
|Definition||Cofactors can define as the non-protein, helper molecules required for the activity of enzymes made of conjugated protein (also called Apoenzymes) that may include the simple metal ions and simple or complex organic groups||Coenzymes can define as the organic co-substrates that are inactive, non-protein part of an enzyme that directly participates in the enzyme catalysis reaction|
|Chemical nature||These can be both organic and inorganic types||These are organic molecules|
|Association with an enzyme||It can covalently or non-covalently associate with an apoenzyme||It binds loosely or non-covalently with an apoenzyme|
|Separation||Separation of cofactors can be easy or difficult (separates only by enzyme denaturation)||Coenzymes are attached transiently to an apoenzyme and can be easily detachable|
|Dialysability||Few are dialysable, while others are non-dialysable||It is dialysable|
|Classification||It is classified into two types based on the enzymatic activity, namely inorganic and organic cofactors||It is a subtype of cofactor comes under the category of organic cofactors|
|Function||These function as the helper molecules that fastens the enzymatic reaction||These function as the substrate shuttles that helps in translocation of atoms or groups|
|Integral part||A cofactor is a collective term that represents activator metal ions, coenzymes, prosthetic groups necessary for an inactive enzyme to function||The integral part of the coenzymes are vitamins|
Definition of Cofactor
It can define as the small, non-protein, helper or accessory molecules that are necessary to bring an inactive apoenzyme to an active state termed as holoenzyme or complete enzyme. Apoenzymes are composed of conjugated proteins, which requires an additional factor to act like a functional enzyme or catalytically active.
An enzyme contains an active site where the substrate binds explicitly to an enzyme and an allosteric site where the allosteric activators and inhibitors can bind particularly to accelerate or inhibit the enzymatic activity. Cofactors can be inorganic (includes metals ions) and organic (includes coenzymes and prosthetic groups) in nature.
According to the chemical nature and association with an enzyme, the cofactors are generally classified into two types.
A large group of metal ions like (Mg 2+, Cu +, Mn 2+ ) are the inorganic cofactors that are essential trace elements in our diet. Enzymes that are activated in association with metal ions are called as metal activated enzymes or metalloenzymes.
In some case, an enzyme needs to be allosterically regulated by the binding of certain inorganic elements. These inorganic elements are generally the effector molecules, but not regarded as cofactors. For instance, calcium participates in the allosteric regulation of nitric oxide synthase, adenylate kinase etc.
Organic cofactors include coenzymes and prosthetic groups, which we will discuss below in the definition of coenzyme.
Definition of Coenzyme
It can define as the co-substrates or secondary substrates that are inactive, non-protein and small organic molecules of low molecular weight (< 1000Da), which directly participates in the enzyme catalytic reactions.
The coenzyme is a subtype of the cofactor molecules that are organic in nature, which assist binding of a substrate molecule to an enzyme’s active site. A coenzyme binds weakly to the inactive protein or apoenzyme, which can be easily separated by dialysis. It plays a conclusive role in an inactive enzyme to function.
As we have discussed, some enzymes need a specific carrier or molecules to catalyse a reaction. Coenzymes works as the co-substrates that binds with the substrate molecules, undergoes some alternation during enzyme activity, and later regenerates or function as a recyclable shuttle.
A prosthetic group is another kind of organic cofactor that are complex organic groups that bind covalently with the protein. Its separation from an enzyme is difficult, as it is only separated by the enzyme denaturation. For instance, heme is a prosthetic group containing an iron atom in the haemoglobin molecule.
There are few examples of the enzymes and their cofactors:
- Fe2+ or Fe3+: Catalase, Peroxidase etc.
- Cu2+: Cytochrome oxidase, superoxide dismutase etc.
- Zn2+: Alcohol dehydrogenase, Carboxypeptidase etc.
- Mg2+: Hexokinase, Enolase, Glucose 6-P
- Mn2+: Arginase, Enolase, Pyruvate carboxylase
- K+: Pyruvate kinase
- Ni2+: Urease
- Mo: Dinitrogenase, Xanthine oxidase
- Se: Glutathione peroxidase
There are few examples of coenzymes of vitamin B-complex:
- Thiamine (B1 vitamin): Thiamine pyrophosphate is the coenzyme of thiamine precursor of vitamin B1 that participates in the decarboxylation, aldehyde group transfer etc.
- Riboflavin (B2 vitamin): FAD and FMN are the flavin molecules that acts as a coenzyme of vitamin B2, and actively participates in the redox reactions.
- Pyridoxine (B6): Pyridoxal phosphate is a coenzyme of pyridoxine precursor of vitamin B6 that carries out amino group transfer.
Key Differences Between Cofactor and Coenzyme
- The alternative names for the term cofactor and coenzyme are helper molecules or accessory molecules and co-substrate or secondary substrate.
- Cofactors can define as the non-protein, helper molecules required for the activity of enzymes made of conjugated protein (also called Apoenzymes) that may include the simple metal ions or the complex organic groups. Coenzymes can define as the non-protein, organic co-substrates that are inactive (without a protein part or apoenzyme), and directly participates in the enzyme catalysis reaction.
- Cofactors are classified into two types based on the enzymatic activity, namely inorganic and organic cofactors. The inorganic cofactors include metal ions, while organic cofactors include coenzymes and prosthetic groups. Thus, the coenzyme is a subtype of the cofactor.
- Cofactors constitute a broad group of accessory elements, in which some can covalently or non-covalently associated with an apoenzyme. Coenzymes are the carrier molecules that join transiently or non-covalently with an apoenzyme.
- The separation of cofactors from an enzyme is sometimes easy or difficult (only separates as a result of enzyme denaturation). As the coenzymes are transiently attached to the enzymes, they are easily separable.
- Dialysability is a property of the ions or molecules that can diffuse down a semipermeable membrane or can be separated by dialysis. Few cofactors are dialysable (Like coenzymes, metal ions), while others are non-dialysable.
- The function of the cofactor is to fasten the enzymatic reaction. Coenzymes works as the substrate shuttles that help in translocation of atoms or groups from one place to the other inside a cell.
Therefore, we can conclude that the cofactor is a collective term that includes inorganic metal ions, organic compounds (coenzymes) and organic prosthetic groups. Coenzymes and cofactors are the additional factors, which facilitate enzyme catalysis by binding with the inactive protein that alone can not bring out the conversion of substrate into product.