Clarifying: What are the co enzymes in vitamin C and its cofactor role?

January 4, 2026 •

2 min read

While commonly referred to as a vitamin, many people misunderstand its fundamental biochemical role, believing it to be a traditional coenzyme. This article clarifies that L-ascorbic acid, or vitamin C, primarily functions as a vital cofactor, not a coenzyme, assisting a family of enzymes critical to human health.

Quick Summary

Vitamin C functions as a cofactor by donating electrons to specific enzymes, aiding vital processes like collagen synthesis, carnitine production, and neurotransmitter formation. It is not a classic coenzyme.

Key Points

Cofactor, not a Coenzyme: Vitamin C primarily acts as a reducing agent cofactor, not a classical coenzyme like those derived from B-vitamins.
Collagen Stabilizer: It is essential for the hydroxylation of proline and lysine by hydroxylase enzymes, stabilizing the collagen triple helix structure.
Energy Production: Vitamin C is a critical cofactor for enzymes involved in the synthesis of carnitine, which transports fatty acids into mitochondria for energy.
Neurotransmitter Aid: The vitamin supports the production of norepinephrine by acting as a cofactor for dopamine beta-hydroxylase.
Epigenetic Regulator: Vitamin C assists TET enzymes in DNA demethylation, influencing gene expression and potentially suppressing tumors.
Antioxidant Function: Its ability to donate electrons also makes vitamin C a potent antioxidant, protecting cells from damaging free radicals.
Iron Reduction: Vitamin C reduces dietary ferric iron to the more absorbable ferrous form, aiding its uptake in the intestine.

Distinguishing a Cofactor from a Coenzyme

In biochemistry, enzymes often require non-protein helper molecules to function. A cofactor is a general term for these molecules or ions. A coenzyme is a specific type of cofactor that is an organic molecule. Vitamin C functions as a cofactor, specifically by donating electrons to keep metal ions at an enzyme's active site in a reduced state. This differs from the role of many coenzymes, which act as carriers for functional groups.

The Cofactor Functions of Vitamin C in Biosynthesis

Vitamin C is an essential cofactor for several enzymes, mainly involved in hydroxylation reactions, which add a hydroxyl (-OH) group.

Collagen Synthesis

Vitamin C is crucial for stabilizing collagen, the body's most abundant protein. It acts as a cofactor for three groups of enzymes (prolyl-3-hydroxylases, prolyl-4-hydroxylases, and lysyl hydroxylases) that hydroxylate proline and lysine residues, a necessary step for forming the stable collagen triple helix. Without sufficient vitamin C, collagen is unstable, leading to the symptoms of scurvy.

Carnitine Synthesis

Vitamin C is a cofactor for enzymes (ε-N-trimethyl-L-lysine hydroxylase and γ-butyrobetaine hydroxylase) needed to synthesize L-carnitine from lysine. Carnitine is vital for transporting fatty acids into mitochondria for energy production. Deficiency can impair fatty acid metabolism and cause fatigue.

Neurotransmitter Synthesis

The nervous system requires vitamin C. It is a cofactor for dopamine beta-hydroxylase, the enzyme that converts dopamine to norepinephrine. Vitamin C also supports the recycling of tetrahydrobiopterin, a cofactor for another enzyme in catecholamine synthesis.

Peptide Hormone Amidation

Vitamin C is required by the enzyme peptidylglycine alpha-amidating monooxygenase (PAM) for the amidation of many peptide hormones and neuropeptides, a process needed for their biological activity.

Hypoxia-Inducible Factor (HIF) Regulation

Vitamin C is a cofactor for HIF-proline dioxygenase enzymes. These enzymes hydroxylate HIF in oxygen-rich conditions, targeting it for degradation. In low oxygen, HIF is not hydroxylated and promotes adaptation.

Epigenetic Regulation

Research shows vitamin C acts as a cofactor for ten-eleven translocation (TET) enzymes, which initiate DNA demethylation. This impacts gene expression and is linked to cellular and developmental processes.

Comparison: Vitamin C (Cofactor) vs. B-Vitamins (Coenzymes)

This table highlights the differences between Vitamin C and typical coenzymes derived from B-vitamins.


Feature	Vitamin C (Ascorbic Acid)	B-Vitamins (e.g., FAD, NAD+)
Classification	Cofactor (reducing agent)	Coenzyme (carrier of functional groups or electrons)
Mechanism	Donates electrons to maintain metal ions in reduced state.	Carries or transfers functional groups or electrons.
Reaction Type	Primarily hydroxylation.	{Link: MDPI https://www.mdpi.com/2075-1729/15/2/238}
Example Enzymes	Prolyl hydroxylase, lysyl hydroxylase.	Pyruvate Dehydrogenase (multiple coenzymes).
Deficiency Result	Impaired collagen (scurvy).	Various symptoms depending on B-vitamin.

Conclusion

Addressing what are the co enzymes in vitamin C, it functions as a cofactor and reducing agent, not a classic coenzyme. Its electron-donating ability is key to its role in processes like producing stable collagen, carnitine, and neurotransmitters. For more information on the enzymes that depend on vitamin C as a cofactor, consult the {Link: Linus Pauling Institute https://lpi.oregonstate.edu/mic/vitamins/vitamin-C}.

Frequently Asked Questions

Vitamin C is called a cofactor because it primarily functions as a reducing agent, maintaining metal ions like iron and copper in a reduced state at an enzyme's active site. A coenzyme, in contrast, typically serves as a carrier for functional groups.

Vitamin C's primary role in collagen synthesis is to act as a cofactor for prolyl and lysyl hydroxylase enzymes. This allows them to add hydroxyl groups to proline and lysine, which is essential for stabilizing the collagen molecule's triple helix structure.

Vitamin C supports energy metabolism by acting as a cofactor for enzymes involved in synthesizing carnitine. Carnitine is necessary for transporting fatty acids into the mitochondria, where they are burned for energy.

Yes, vitamin C is important for brain function. It is concentrated in brain tissues and acts as a cofactor for dopamine beta-hydroxylase, an enzyme that produces the neurotransmitter norepinephrine.

A severe vitamin C deficiency can lead to scurvy. Symptoms include fatigue, muscle weakness, and problems with connective tissues like sore gums and poor wound healing, all due to impaired collagen synthesis.

Yes, vitamin C can influence gene expression by acting as a cofactor for TET enzymes, which are involved in the process of DNA demethylation. This epigenetic effect can modulate transcription and influence cell behavior.

Yes, vitamin C enhances the absorption of non-heme iron from plant-based foods. It does this by reducing ferric iron to the more readily absorbed ferrous state in the intestine.

Yes, vitamin C can assist other biological molecules. For example, it helps regenerate the antioxidant form of vitamin E after it has neutralized free radicals.