Antioxidant Enzyme Systems

There are several enzyme systems that catalyze reactions to neutralize free radicals and reactive oxygen species. These enzymes include:

  • superoxide dismutase
  • glutathione peroxidise
  • glutathione reductase
  • catalases

These form the body’s endogenous defence mechanisms to help protect against free radical-induced cell damage. The antioxidant enzymes – glutathioneperoxidase, catalase, and superoxide dismutase (SOD) – metabolize oxidative toxic intermediates.

These enzymes also require co-factors such as selenium, iron, copper, zinc, and manganese for optimum catalytic activity. It has been suggested that an inadequate dietary intake of these trace minerals may compromise the effectiveness of these antioxidant defense mechanisms. The consumption and absorption of these important trace minerals may decrease with aging.

Glutathione enzymes and system

Glutathione, an important water-soluble antioxidant, is synthesized from the amino acids glycine, glutamate, and cysteine. Glutathione can directly neutralize ROS such as lipid peroxides, and also plays a major role in xenobiotic metabolism.

Xenobiotics are toxins that the body is exposed to. Exposure of the liver to xenobiotic substances means the body prepares itself by increasing detoxification enzymes, i.e., cytochrome P-450 mixed-function oxidase.

When an individual is exposed to high levels of xenobiotics, more glutathione is utilized for conjugation. Conjugation with Glutathioone renders the toxin neutral and makes it less available to serve as an antioxidant. Research suggests that glutathione and vitamin C work interactively to neutralize free radicals. These two also have a sparing effect upon each other.

The glutathione system includes glutathione, glutathione reductase, glutathione peroxidases and glutathione ''S''-transferases. Of these glutathione peroxidase is an enzyme containing four selenium-cofactors that catalyzes the breakdown of hydrogen peroxide and organic hydroperoxides. Glutathione ''S''-transferases show high activity with lipid peroxides. These enzymes are at particularly high levels in the liver.

Lipoic acid

This is another important endogenous antioxidant. It is categorized as “thiol” or “biothiol”. These are sulfur-containing molecules that catalyze the oxidative decarboxylation of alpha-keto acids, such as pyruvate and alphaketoglutarate, in the Krebs cycle.

Lipoic acid and its reduced form, dihydrolipoic acid (DHLA), neutralize the free radicals in both lipid and aqueous domains and as such has been called a “universal antioxidant.”

Superoxide dismutase

Superoxide dismutases (SODs) are a class of enzymes that catalyse the breakdown of the superoxide anion into oxygen and hydrogen peroxide. These enzymes are present in almost all aerobic cells and in extracellular fluids.

SODs contain metal ion cofactors that, depending on the isozyme, can be copper, zinc, manganese or iron. For example, in humans copper/zinc SOD is present in the cytosol, while manganese SOD is present in the mitochondrion. The mitochondrial SOD is most biologically important of these three.

In plants, SOD isozymes are present in the cytosol and mitochondria. There is also an iron SOD found in chloroplasts.


Catalases are enzymes that catalyse the conversion of hydrogen peroxide to water and oxygen, using either an iron or manganese cofactor. This is found in peroxisomes in most eukaryotic cells. Its only substrate is hydrogen peroxide. It follows a ping-pong mechanism.

Here, its cofactor is oxidised by one molecule of hydrogen peroxide and then regenerated by transferring the bound oxygen to a second molecule of substrate.


There are peroxidases that catalyze the reduction of hydrogen peroxide, organic hydroperoxides, as well as peroxynitrite. These may be of three basic types - typical 2-cysteine peroxiredoxins; atypical 2-cysteine peroxiredoxins; and 1-cysteine peroxiredoxins. Peroxiredoxins seem to be important in antioxidant metabolism.

Further Reading

Last Updated: Jul 5, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Mandal, Ananya. (2023, July 05). Antioxidant Enzyme Systems. News-Medical. Retrieved on July 23, 2024 from

  • MLA

    Mandal, Ananya. "Antioxidant Enzyme Systems". News-Medical. 23 July 2024. <>.

  • Chicago

    Mandal, Ananya. "Antioxidant Enzyme Systems". News-Medical. (accessed July 23, 2024).

  • Harvard

    Mandal, Ananya. 2023. Antioxidant Enzyme Systems. News-Medical, viewed 23 July 2024,


  1. AM Angotti AM Angotti United States says:

    Hello, So i can take sod ,glutathione and the other cofactors for the best benefits?? Ty

  2. Eben Burger Eben Burger Malaysia says:

    Fantaatic. Thank you. Simple and clearly explained. What lead me to this article was my curiosity to learn more about Hydroxyl Radicals. I'm still a bit confused but it seems that they are formed when H202 react with either Fe or Cu. What's interesting is that apparently they are more prevalent when the body runs out of an adequate amount of SOD, CAT ETC.... Which I guess is why Hydroxyl Radicals are a major problem in Diabetics. Also interestingly Both STZ and Alloxan used as Diabetogens in Lab rats are Primarily Known as powerful Hydroxyl Radicals. It seems that There are many Hydroxyl radical scavengers such as Vit C, Garlic, Chili, Papaya seeds, and flavonoids in Foods. I conclude that In the case of Diabetes its crucial to make sure you have adequate Mineral intake such as Zn, Se, Cu, Fe, Mn, As well as both water and fat soluble Vitamins such as vit A, B, and C. Many herbs contain powerful natural antioxidants. Green juices are high in Vitamins. Fermented Seeds are high in Digestable minerals and healthy fats...
    This is really a fascinating subject. Lastly, what interests me is the fact that a compromised immune system - such as a compromised endogenous Antioxidant Enzyme system and nutrientdediciencies - Causes an individual to be prone to more Bacteriall, Fungal, and Viral and Parasitic enfections that ALSO by themselves indirectly further tax needed Antioxidants and Nutrients making the illness much worse than before. So in treating the illness, NOW you ALSO have to treat the Fungal, viral or Parasitic conditions AND address the Nutrient DEFICIENCIES. All this is really interesting but REALLY CRAZY. It's a daunting task!

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Eating baby carrots three times a week raises skin carotenoid levels in young adults