Nickel-urease (urease, EC 3.5.1.5) is a metalloenzyme that catalyzes the hydrolysis of urea (NH₂-CO-NH₂) to Ammonia (NH₃) and carbon dioxide (CO₂). The active site contains two nickel ions (nickel (Ni)²⁺) coordinated by Histidine and cysteine residues.

Nickel-urease is expressed by H. pylori as a critical virulence factor enabling survival in the acidic gastric environment; it is also found in soil bacteria and some oral pathogens.

For H. pylori, urease is the Achilles' heel: nickel starvation disables urease, and urease inhibitors or nickel chelation can reduce bacterial load. This makes nickel-urease a prime target for both therapeutic intervention and microbiota-targeted metallomics.

Contents1. Mechanism2. Role in Disease3. Metal Connections4. Connections

Mechanism#

Urea hydrolysis and ammonia production:

H. pylori lives in the stomach (pH 1.5–2). The gastric mucus layer is acidic. Ammonia-producing urease provides local pH buffering:

`` H. pylori + urea (via urease) → NH₃ + CO₂ + H₂O NH₃ + H⁺ → NH₄⁺ (ammonium, pKa 9.25) ``

Even modest ammonia production (locally around the bacterium) raises pH from 2 to ~4–5, creating a microenvironment permissive for survival and motility. Without urease, H. pylori is killed by gastric acid within minutes.

Nickel coordination in the active site:

Urease requires two nickel (Ni)²⁺ per active site. The nickel atoms are. Bridged by a hydroxyl group.

Coordinated by histidine and cysteine residues. Functionally important for substrate binding and catalytic turnover.

Nickel acquisition. H. pylori encodes a Nickel permease nixa to transport nickel²⁺ from the hostile gastric environment. In the cytoplasm, accessory proteins (ured, uree, uref, ureg) insert nickel into the urease apoprotein during maturation.

Mutations in these maturation factors → catalytically inactive urease → loss of virulence.

Role in Disease#

H. pylori-associated gastric disease. Gastric Ulcer: H. pylori colonization → urease-driven ammonia → local pH buffering → epithelial invasion and Metal-Driven Inflammation → ulcer formation. Gastric Adenocarcinoma: Chronic H. pylori infection (urease-mediated persistence) → chronic atrophic gastritis → intestinal metaplasia → gastric cancer (WHO Group 1 carcinogen).

malt-lymphoma (mucosa-associated lymphoid tissue lymphoma): Indolent B-cell lymphoma driven by chronic H. pylori antigen stimulation; urease is an immunogen. Dyspepsia and functional gastric disease: H. pylori-negative dyspepsia may be associated with other urease-producing bacteria (Proteus mirabilis, Klebsiella pneumoniae).

Urease as biomarker. Urease breath test (UBT): Diagnostic gold standard for H. pylori. Patient ingests ¹³C- or ¹⁴C-labeled urea; if H. pylori is present, urease cleaves it → labeled CO₂ is absorbed and exhaled → detected in breath.

This is the most accurate non-invasive H. pylori test.

Metal Connections#

Nickel-urease exemplifies Primitive 4: Microbial Metal Dependencies as Achilles' Heels:

Nickel requirement. H. pylori CANNOT survive without urease (no other catabolic pathway to survive gastric acid). Urease CANNOT function without two nickel (Ni)²⁺ per active site (unlike many enzymes with loosely-bound cofactors).

Therefore: Nickel starvation → urease inactivation → H. pylori eradication.

Nickel bioavailability in the stomach. Gastric pH (1.5–2) solubilizes nickel; nickel²⁺ is biologically available. H. pylori NixA permease transports nickel²⁺ against concentration gradient.

Nickel chelators (EDTA, dithiocarbamate) in gastric juice may limit nickel availability and reduce H. pylori colonization density.

Cross-talk with Iron and Zinc. Iron-dependent enzymes: H. pylori also produces Iron-dependent catalase and superoxide dismutase; dual metal starvation (nickel + iron) is more potent than single-metal depletion. Zinc: Host Zinc-dependent immune functions (Th1 differentiation, neutrophil recruitment) oppose H. pylori; zinc deficiency worsens infection.

Connections#

Related enzymes. NiFe-Hydrogenase—another nickel-iron enzyme used by H. pylori (and sulfate-reducing bacteria) for anaerobic energy metabolism. Zinc-Metalloprotease—H. pylori's vacuolating cytotoxin (VacA) is a zinc-dependent protease; complements urease virulence.

Related organisms. Helicobacter pylori—the primary pathogen expressing nickel-urease. Proteus mirabilis—soil bacterium; also urease-positive; causes urinary tract infections via urease-driven ammonia and crystal formation. Klebsiella pneumoniae—urease-positive; can cause gastric and respiratory infections.

—H. pylori-like species in oral cavities; urease-positive.

Related concepts. Nutritional Immunity (Metal Sequestration)—nickel starvation as a host defense mechanism. metal-cofactor-dependency—general principle of which urease is an example.—gastric niche where urease enables survival.

—complementary H. pylori virulence factor.

Related metals. Nickel—the essential cofactor; nickel depletion is therapeutic strategy. Iron—H. pylori expresses iron-dependent catalase; dual-metal targeting increases efficacy.

Disease pages. ,—H. pylori-driven conditions where urease is the enabling virulence factor.

Generated evidence record

References 8

Numbered by first appearance in the article, then reconciled with its declared source list.

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    Denise Mafra, Natalia A. Borges, Livia Alvarenga et al. (2022). Fermented Food: Should Patients with Cardiometabolic Diseases Go Back to an Early Neolithic Diet?. Critical Reviews in Food Science and Nutrition.

  2. 2

    Benoit, S.L., Bhatt et al. (2021). Benoit & Maier 2021 — Nickel Chelator Inhibits Amyloid-Beta Aggregation. Scientific Reports.

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    Benoit SL, Bhatt RJ, Maier RJ (2021). The nickel-chelator dimethylglyoxime inhibits human amyloid beta peptide in vitro aggregation. Scientific Reports.

  4. 4

    Yuqi Wu, Oscar Wong, Sizhe Chen et al. (2025). Wu 2025 — Distinct Diet-Microbiome Associations in Autism Spectrum Disorder. Nature Communications.

  5. 5

    Swierc J, Drzymala S, Wozniak D et al. (2022). The influence of nickel on intestinal microbiota disturbances. Pomeranian Journal of Life Sciences.

  6. 6

    Karen Pendergrass (2026). Pendergrass 2026 — Endometriosis Conference Presentation (Amsterdam). Conference Presentation.

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    ★Patil RH, Luptakova D, Havlicek V (2021). Infection metallomics for critical care in the post-COVID era. Mass Spectrometry Reviews.

  8. 8

    Genchi G, Carocci A, Lauria G et al. (2020). Genchi 2020 — Nickel: Human Health and Environmental Toxicology. International Journal of Environmental Research and Public Health.

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Article network

Current recordNickel-UreaseMechanisms
MechanismsAmmoniaReferenced in this mechanisms recordMechanismsHistidineReferenced in this mechanisms recordMicroorganismsHelicobacter pyloriReferenced in this mechanisms recordMetalsNickelReferenced in this mechanisms recordMechanismsNickel TransportersReferenced in this mechanisms recordMechanismsUreaseReferenced in this mechanisms recordDiseasesGastric UlcerReferenced in this mechanisms recordHost defensesMetal-Driven InflammationReferenced in this mechanisms recordDiseasesGastric AdenocarcinomaReferenced in this mechanisms recordMicroorganismsProteus mirabilisReferenced in this mechanisms recordMicroorganismsKlebsiella pneumoniaeReferenced in this mechanisms recordMechanismsEDTAReferenced in this mechanisms record
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