Which of the following enzymes require ascorbate vitamin C for its activity?

December 17, 2025 •

4 min read

While most animals can produce their own vitamin C, humans cannot, making dietary intake essential for over 15 known enzymatic reactions. A deficiency in ascorbate, the active form of vitamin C, leads to a dysfunction in several critical enzymes that require it as a cofactor for their activity. These enzymes govern processes ranging from connective tissue formation to neurotransmitter synthesis.

Quick Summary

Several enzymes depend on ascorbate (vitamin C) to function properly, including hydroxylases crucial for collagen and carnitine production, dopamine beta-hydroxylase for neurotransmitter synthesis, and dioxygenases involved in epigenetic regulation.

Key Points

Collagen Synthesis: Prolyl and lysyl hydroxylases are ascorbate-dependent enzymes critical for forming stable, cross-linked collagen, which is essential for healthy connective tissue, bones, and skin.
Fat Metabolism: Enzymes such as trimethyllysine hydroxylase and gamma-butyrobetaine hydroxylase require ascorbate for the biosynthesis of carnitine, which is necessary for transporting fatty acids into mitochondria for energy.
Neurotransmitter Production: Dopamine beta-hydroxylase needs ascorbate as a cofactor to convert dopamine into norepinephrine, affecting mood and the stress response.
Epigenetic Regulation: The TET and JmjC families of dioxygenases require ascorbate to demethylate DNA and histones, respectively, thereby influencing gene expression.
Hormone Amidation: Peptidylglycine alpha-amidating monooxygenase (PAM) uses ascorbate to create active peptide hormones and neurotransmitters.
Redox Function: Ascorbate maintains iron and copper ions in their active, reduced state within these enzymes, making its electron-donating properties key to their function.

Ascorbate-Dependent Enzymes in Biological Pathways

Ascorbate, or vitamin C, plays a vital role as a cofactor for a family of enzymes known as hydroxylases and oxygenases. Its primary function in these reactions is to maintain the necessary metal ions, typically iron ($Fe^{2+}$) or copper ($Cu^{2+}$), in their reduced state at the enzyme's active site. Without sufficient ascorbate, the metal ion can become oxidized, halting enzyme function and impairing crucial biochemical pathways throughout the body.

Enzymes Crucial for Collagen Synthesis

Collagen is the most abundant protein in the human body, providing structural integrity to connective tissues like skin, bone, tendons, and cartilage. The proper formation of its strong, triple-helix structure is entirely dependent on the hydroxylation of specific proline and lysine amino acid residues, a process that requires ascorbate.

Prolyl hydroxylase: These enzymes, including prolyl-3-hydroxylase and prolyl-4-hydroxylase, catalyze the addition of hydroxyl groups to proline residues in procollagen. This hydroxylation is necessary for the collagen helix to fold correctly, giving it stability and tensile strength.
Lysyl hydroxylase: Also known as procollagen-lysine 5-dioxygenase, this enzyme adds hydroxyl groups to lysine residues. These hydroxylated lysines are essential for the formation of cross-links between collagen fibers, further strengthening the connective tissue.

Enzymes for Carnitine Production

Carnitine is a molecule vital for energy metabolism, as it transports long-chain fatty acids into the mitochondria for oxidation. Its biosynthesis from the amino acid lysine involves a series of enzymatic steps, two of which are ascorbate-dependent hydroxylations.

Trimethyllysine hydroxylase (or epsilon-N-trimethyl-L-lysine hydroxylase): This enzyme catalyzes the first of two hydroxylation steps in the conversion of trimethyllysine to carnitine.
Gamma-butyrobetaine hydroxylase: This enzyme, specifically gamma-butyrobetaine, 2-oxoglutarate dioxygenase, facilitates the final hydroxylation step, converting gamma-butyrobetaine into carnitine. A deficiency in ascorbate can significantly reduce carnitine levels, leading to fatigue.

Enzymes for Neurotransmitter and Hormone Synthesis

Ascorbate is a necessary cofactor for several enzymes involved in the nervous and endocrine systems, influencing mood, stress response, and hormone activity.

Dopamine beta-hydroxylase: This enzyme is responsible for converting the neurotransmitter dopamine to norepinephrine, a critical step in the biosynthesis of catecholamines. It is a copper-containing enzyme that relies on ascorbate to remain active.
Peptidylglycine alpha-amidating monooxygenase (PAM): This enzyme is involved in the amidation of various peptide hormones and neurotransmitters, which increases their stability and biological activity. The reaction requires ascorbate as a cofactor.

Enzymes Involved in Epigenetic Regulation

Beyond its role in biosynthesis, ascorbate also functions in epigenetic modification by supporting enzymes that regulate gene expression.

Ten-eleven translocation (TET) family of dioxygenases: TET enzymes catalyze the oxidation of 5-methylcytosine, initiating a pathway for DNA demethylation. This is a fundamental process in cellular reprogramming and has implications for cancer biology.
Jumonji-C (JmjC) domain-containing histone demethylases: These enzymes participate in the demethylation of histone proteins. Since histones are involved in gene transcription, this process is critical for regulating gene expression.

Comparison of Ascorbate-Dependent Enzyme Pathways


Pathway	Key Enzymes Requiring Ascorbate	Core Biological Function	Consequence of Deficiency	Associated Disease/Condition
Collagen Synthesis	Prolyl and Lysyl Hydroxylases	Stabilizes collagen's triple-helix structure	Defective collagen cross-linking and connective tissue weakening	Scurvy, poor wound healing, bleeding gums
Carnitine Biosynthesis	Trimethyllysine and Gamma-butyrobetaine Hydroxylases	Transports fatty acids for mitochondrial energy production	Reduced energy metabolism, fatigue, muscle weakness	Fatigue, decreased exercise tolerance
Neurotransmitter Synthesis	Dopamine beta-hydroxylase (DBH)	Converts dopamine to norepinephrine	Impaired synthesis of catecholamines like norepinephrine	Mood disturbances, neurological deficits
Hormone Amidation	Peptidylglycine Alpha-Amidating Monooxygenase (PAM)	Activates peptide hormones	Reduced activity of critical hormones like vasopressin	Hormonal imbalances, impaired fluid balance
Epigenetic Regulation	TET and JmjC Dioxygenases	Demethylates DNA and histones to regulate gene expression	Epigenetic abnormalities, impaired cellular reprogramming	Links to cancer and developmental issues

Conclusion: The Broad Importance of Ascorbate

Ascorbate's function as an essential enzyme cofactor is far-reaching, encompassing fundamental processes like structural protein formation, energy metabolism, and even the regulation of gene expression. The family of hydroxylase and oxygenase enzymes that rely on ascorbate for their activity underscores its crucial role in maintaining human health. From the integrity of connective tissues maintained by prolyl and lysyl hydroxylases to the proper functioning of the nervous and endocrine systems via enzymes like dopamine beta-hydroxylase, ascorbate is indispensable. The severe symptoms of scurvy—a direct result of insufficient ascorbate—are a powerful testament to the widespread metabolic consequences of a deficiency. Modern research continues to uncover new epigenetic roles for ascorbate, confirming its deep and continuous impact on cellular function. A consistent dietary intake is therefore critical, not just for preventing deficiency diseases, but for supporting the optimal function of these vital enzymatic pathways.

Additional Resources

For a detailed list and explanation of enzymes that require vitamin C, the Linus Pauling Institute at Oregon State University offers comprehensive information(https://lpi.oregonstate.edu/mic/vitamins/vitamin-C).

Frequently Asked Questions

Ascorbate acts as a reducing agent, donating electrons to maintain the necessary metal ions (such as iron or copper) in their active, reduced state at the enzyme's core.

Ascorbate is essential for prolyl and lysyl hydroxylase enzymes, which hydroxylate proline and lysine residues in collagen. This process allows the collagen to form a stable triple-helix structure.

The enzyme dopamine beta-hydroxylase, which contains copper, uses ascorbate as a cofactor to catalyze the conversion of dopamine to norepinephrine.

Ascorbate is required for two enzymes involved in the synthesis of carnitine, which transports fatty acids into mitochondria for energy production. Without enough ascorbate, carnitine production slows down, potentially leading to fatigue.

Yes, ascorbate is a cofactor for dioxygenases like the TET and JmjC families, which are involved in epigenetic processes such as DNA and histone demethylation, influencing gene expression.

Without sufficient ascorbate, the metal ions in the enzymes become oxidized and inactive. The enzymatic reaction halts, leading to impaired functions like defective collagen synthesis or reduced neurotransmitter production.

Not all hydroxylases, but a large family of them, particularly those dependent on iron or copper, require ascorbate to maintain the metal ion in its reduced, active state.