82 by: Thamindu Widyaratne

Student – Thamindu Widyaratne

Enzyme – Xanthine Oxidase

E.C. # – 1.17.3.2

Xanthine oxidase is found in mammals, and was first discovered in mammalian milk. XO is produced in the hepatocytes of the liver. Some XO is secreted into the gastrointestinal tract, while the rest remains in the hepatocyte’s cytosol. XO is also added to blood serum via hepatic cell turnover, where the enzymes of dead hepatocytes are released into the bloodstream.

Fun facts and important information:

• – Xanthine oxidase is non-specific, and will oxidate certain other purines, pterins, and aldehydes. Due to XO’s non-specific action, it was initially thought that XO was two enzymes. In 1902, Franz Schardinger demonstrated that milk contains an enzyme which oxidizes aldehydes into acids. This was called “Schardinger’s enzyme.” 20 years later, E.J. Morgan demonstrated that milk contained an enzyme which oxidizes hypoxanthine into xanthine, which was named xanthine oxidase. It would take 16 more years for these enzymes to be recognized as one and the same.
• – Reduction of xanthine oxidase turns it into the similar enzyme xanthine dehydrogenase (E.C. 1.17.1.4), which acts on the same substrates but uses NAD as an oxidizing agent. This results in NADH and H+ being produced rather than H2O2. Xanthine dehydrogenase can be oxidized back into XO. Xanthine dehydrogenase is the form primarily found in animals.
• – Overabundance of xanthine oxidase can lead to uric acid being produced in the body faster than it can be removed. The toxic buildup of uric acid in the body can lead to the deposition of uric acid crystals in the body, causing gout. Gout is prevented and treated with the competitive xanthine oxidase inhibitor allopurinol.

REFERENCES

Bortolotti, M., Polito, L., Battelli, M. G., & Bolognesi, A. (2021). Xanthine oxidoreductase: One enzyme for multiple physiological tasks. Redox Biology, 41, 101882. https://doi.org/10.1016/j.redox.2021.101882

Kostić, D. A., Dimitrijević, D. S., Stojanović, G. S., Palić, I. R., Đorđević, A. S., & Ickovski, J. D. (2015). Xanthine oxidase: Isolation, assays of activity, and inhibition. Journal of Chemistry, 2015, 1–8. https://doi.org/10.1155/2015/294858

O’Neill, M. J. F., & McKusick, V.A. (2016). Xanthine Dehydrogenase; XDH. Online Mendilian Inheritance In Man.

Xanthinuria—An overview | sciencedirect topics. (n.d.). Retrieved October 17, 2024, from https://www.sciencedirect.com/topics/medicine-and-dentistry/xanthinuria