Urease is an enzyme, a biological catalyst, found widely in nature across various organisms and environments. It facilitates the breakdown of urea, a nitrogen-containing compound. This enzyme is involved in numerous biological processes, accelerating the decomposition of urea, and is estimated to break down over 10 million tons of urea annually.
How Urease Works
Urease catalyzes the hydrolysis of urea, a chemical reaction where water breaks down urea. This process converts urea ((NH₂)₂CO) into two molecules of ammonia (NH₃) and one molecule of carbon dioxide (CO₂). The reaction occurs in two stages: first, ammonia and carbamic acid are produced, then carbamate rapidly and spontaneously breaks down into another ammonia molecule and carbonic acid. The production of ammonia is particularly significant because ammonia is a weak base. As ammonia accumulates, it increases the pH of the surrounding environment, making it more alkaline. The enzyme is a metalloenzyme, containing two nickel (Ni²⁺) ions in its active site, which are necessary for its catalytic function.
Where Urease is Found
Urease is broadly distributed throughout nature, found in various organisms and ecosystems. It is present in many bacterial species, including Helicobacter pylori, which colonizes the human stomach, and bacteria associated with urinary tract infections like Proteus mirabilis. Over 90% of clinical methicillin-resistant Staphylococcus aureus strains are also capable of urea hydrolysis. The enzyme is also abundant in various plants, particularly legumes such as soybeans and jack beans, where it is located in the cytoplasm. In plants, urease plays a role in nitrogen metabolism, helping to recycle nitrogen from compounds like arginine, especially during germination. Urease is also present in fungi and is a common enzyme found in soil, contributing to the nitrogen cycle.
The Significance of Urease
Urease is of considerable importance across medical, environmental, and industrial fields.
Medical Significance
In human health, Helicobacter pylori utilizes urease to survive the stomach’s highly acidic environment. It converts urea into ammonia, which neutralizes the surrounding acid and creates a more hospitable niche for the bacterium. This urease activity by H. pylori is linked to conditions like gastritis, peptic ulcers, and can contribute to gastric cancer.
Urease-producing bacteria, such as Proteus mirabilis, are a common cause of urinary tract infections (UTIs) and can lead to the formation of kidney stones, specifically struvite stones. These bacteria break down urea in urine, increasing its pH and promoting the crystallization of magnesium ammonium phosphate and calcium phosphate.
Medically, the presence of urease is leveraged in diagnostic tests. For example, the urea breath test detects H. pylori infections by measuring carbon dioxide produced after a patient ingests carbon-labeled urea.
Environmental and Agricultural Significance
In environmental and agricultural contexts, urease is a significant component of the global nitrogen cycle. It converts urea-based fertilizers applied to soil into ammonia, which plants can absorb as a nitrogen source. However, this conversion can also lead to ammonia volatilization, where ammonia gas escapes into the atmosphere, reducing fertilizer efficiency and contributing to air pollution. To mitigate these losses, urease inhibitors are sometimes used with fertilizers to slow the enzyme’s activity.
Industrial Applications
Urease has industrial applications. It is used in biosensors designed to detect urea levels in various substances, including water, blood, and urine, by measuring pH change or carbon dioxide production. Urease-producing microorganisms can also be employed in bioremediation efforts to remove urea from contaminated water and soil, assisting in wastewater treatment processes for industrial and agricultural runoff.