Difference Between Cofactor and Coenzyme

The difference between cofactor and coenzyme is mainly characterized based on chemical nature and function. Cofactors constitute a large group of helper molecules (inorganic or organic). Conversely, cofactors are small organic molecules.

Coenzymes significantly act as carrier materials to convert the inactive protein (the apoenzyme) into the active form (holoenzyme). In contrast, cofactors serve as biocatalysts that only fasten the enzymatic reaction inside a cell.

Both cofactor and coenzyme are important terms to study the general properties of an enzyme. It is important to note that cofactors or coenzymes only attach to the types of conjugated enzymes containing a non-protein region.

Hence, simple enzymes containing amino acids do not require any additional carriers to show their catalytic activity. This post discusses the key differences between the cofactor and coenzyme, along with the comparison chart, definitions and examples of the two.

Content: Cofactor Vs Coenzyme

1. Comparison Chart
2. Definition
3. Examples
4. Key Differences
5. Conclusion

Comparison Chart

Properties	Cofactor	Coenzyme
Alternative names	Helper molecules or accessory molecules	Co-substrate or secondary substrate
Definition	Cofactors refer to the non-protein helper molecules required for the activity of apoenzymes or enzymes made of conjugated proteins, which may include simple metal ions or complex organic groups	Coenzymes refer to the inactive non-protein organic co-substrates (without a protein part or apoenzyme) that directly participate in the enzyme catalysis
Chemical nature	Cofactors can be organic and inorganic molecules	Cofactors 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 after enzyme denaturation)	Coenzymes are attached transiently to an apoenzyme and can be easily detachable
Dialysability	Few cofactors 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 that comes under the category of organic cofactors
Function	It functions as the helper molecule that fastens the enzymatic reaction	It functions as the substrate shuttle that helps in translocating 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 refers to the small, non-protein, helper or accessory molecule necessary to bring an inactive apoenzyme to an active state termed holoenzyme or complete enzyme. Apoenzymes are conjugated proteins, which require an additional factor to act like a functional or catalytically active enzyme.

An enzyme contains an active site where the specific substrate binds firmly. Oppositely, the allosteric site is the region 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).

According to the chemical nature and association with an enzyme, the cofactors are classified into two types.

1. A large group of metal ions like (Mg 2+, Cu +, Mn 2+) are inorganic cofactors that serve as essential trace elements in our diet. Enzymes that activates in association with metal ions are called metal activated enzymes or metalloenzymes.
2. In some cases, an enzyme needs to be allosterically regulated by the binding of certain inorganic elements. Here, the inorganic elements are generally effector molecules but not regarded as cofactors. For instance, calcium participates in the allosteric regulation of nitric oxide synthase, adenylate kinase etc.
3. Organic cofactors include coenzymes and prosthetic groups, which we will discuss below in the definition of coenzyme.

Definition of Coenzyme

It refers to the co-substrate or secondary substrate that constitutes a group of inactive, non-protein and small organic molecules of low molecular weight (< 1000Da). They directly participate in the enzyme catalytic reactions.

The coenzyme is a subtype of cofactor molecules, which are organic in nature and assists in binding a substrate molecule to an enzyme’s active site. Coenzymes bind 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. Thus, the coenzyme works as a co-substrate that primarily binds with the substrate molecules, undergoes some alternation during enzyme activity, and later regenerates or functions as a recyclable shuttle.

Prosthetic groups are complex organic groups that bind covalently with the protein. Their separation from an enzyme is difficult, or they only separate by the enzyme denaturation. For instance, heme is a prosthetic group containing an iron atom in the haemoglobin molecule.

Cofactor Examples

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

Coenzyme Examples

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, which actively participate in the redox reactions.
• Pyridoxine (B6): Pyridoxal phosphate is a coenzyme of pyridoxine precursor of vitamin B6 that carries out amino group transfer.

Conclusion

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 that facilitate enzyme catalysis by binding with the inactive protein that alone can not convert substrate into product.