80 by: Ella Colistro

Student – Ella Colistro

Enzyme Name – Urease

E.C. Number – 3.5.1.5

Where is the enzyme found? Urease is found in abundance in a variety of bacteria, fungi, plant seeds, and some animal tissues. It is an especially key enzyme in pathogenic bacteria due to its toxic effects on human cells. The products produced by the reaction it catalyzes are toxic to human tissues, and an abundance of these products in the body is known to have a role in the cause of some long-lasting diseases (Konieczna et al., 2012).

What does the enzyme do? Urease catalyzes the hydrolysis of urea into ammonia and carbamate. Urease enzymes consist of two or three subunits, depending on the organism they’re present in. The active site is located in the largest subunit and contains two nickel ions that are involved in binding a urea molecule and a water molecule in the active site. A series of deprotonations is the first step of this mechanism. Asp221 deprotonates His219 which deprotonates urea. His320 then deprotonates the water molecule which nucleophilically attacks the urea. A carbonyl oxygen is then reformed on the urea molecule, which causes the carbon-nitrogen bond to break releasing NH2-. The NH2- then deprotonates His320 forming ammonia. This leaves a carbamate molecule which then dissociates from the active site and spontaneously converts into carbon dioxide and another ammonia molecule. Overall, urease catalyzes the hydrolysis of urea into ammonia and carbamate, and then carbamate spontaneously dissociates into ammonia and carbon dioxide. This means the products of this reaction are two ammonia molecules and one carbon dioxide molecule This reaction increases the basicity of the environment because ammonia is a basic compound (Holliday et al., 2024).

Interesting facts and important information – Urease was the first enzyme to be purified and crystallized. It was also the first enzyme discovered to contain nickel ions. Urease only catalyzes the hydrolysis of urea into ammonia and carbamate, not the dissociation of carbamate into ammonia and carbon dioxide (Holliday et al., 2024). There is a urease test that can be done on bacteria to identify if they are capable of hydrolyzing urea. The test involves a media with phenol red indicator that changes colour from yellow to pink above pH 8.4. If urease is present in a microorganism, then the addition of urea will cause the microorganism to hydrolyze the urea into ammonia which raises the pH due to its basic nature and causes a colour change (University of Wyoming, n.d.).

References

Holliday, G.L., Bartlett, G.J., Almonacid, D.E., Waters, A., Porter, C. (2024). Mechanism and Catalytic Site Atlas: Urease. EMBL-EBI. https://www.ebi.ac.uk/thornton-srv/m-csa/entry/87/.

Huang, J.Y., Sweeny, E.G., Sigal, M., Zhang, H.C., Remington, S.J., Cantrell, M.A., Kuo, C.J., Guillemin, K., Amieva, M.R. (2015). Chemodetection and Destruction of Host Urea Allows Heliobacer pylori to Locate the Epithelium. Cell Host and Microbe, 18(2), 147-156. 10.1016/j.chom.2015.07.002

John Hopkins Medicine. (2024). Conditions and Diseases: Helicobacter Pylori. https://www.hopkinsmedicine.org/health/conditions-and-diseases/helicobacter-pylori

Konieczna, I., Zarnowiec, P., Kwinkowski, M., Kolesinska, B., Fraczyk, J., Kaminski, Z., Kaca, W. (2012). Bacterial urease and its role in long-lasting human diseases. Current Protein and Peptide Science, 13(8), 789–806. https://doi.org/10.2174/138920312804871094

University of Wyoming. Urease test. (n.d.). https://www.uwyo.edu/molb2021/additional_info/summ_biochem/urease.html