Q.91 Urease enzyme catalyzes the conversion of urea into ammonia and carbon dioxide.
Which one of the following organisms expresses urease enzyme?
(A) Caenorhabditis elegans
(B) Drosophila melanogaster
(C) Helicobacter pylori
(D) Homo sapiens

Helicobacter pylori expresses the urease enzyme, making it the correct answer among the options. Urease catalyzes urea hydrolysis into ammonia and carbon dioxide, aiding bacterial survival in acidic environments. This multiple-choice question tests knowledge of urease distribution in model organisms.

Option Analysis

Caenorhabditis elegans (A): This nematode lacks urease enzyme expression. Studies on C. elegans focus on other enzymes like 3-ureidopropionase or aminopeptidases, but no urease activity appears in its genome or metabolic pathways.​

Drosophila melanogaster (B): Fruit flies do not produce urease. They express urate oxidase in Malpighian tubules for uric acid metabolism via the uricolytic pathway, bypassing urea hydrolysis.​

Helicobacter pylori (C): This gastric bacterium produces abundant urease as a key virulence factor. The enzyme, encoded by ureA and ureB genes, forms a 550 kDa multimeric complex that neutralizes stomach acid by generating ammonia, enabling colonization.​

Homo sapiens (D): Humans do not express functional urease. Urea from protein metabolism is excreted by kidneys without hydrolysis; urease activity comes from gut microbiota, not human cells.​

Introduction to Urease Enzyme

Urease enzyme organisms like Helicobacter pylori catalyze urea conversion to ammonia and carbon dioxide, crucial for nitrogen metabolism and pathogenesis. This nickel-dependent metalloenzyme (EC 3.5.1.5) hydrolyzes urea rapidly, producing a local pH-neutralizing cloud around bacteria in acidic environments.​

Urease in Helicobacter pylori

Helicobacter pylori expresses high levels of urease, essential for stomach colonization. The ureAB gene cluster encodes structural subunits UreA (26.5 kDa) and UreB (60-61 kDa), forming a cytoplasmic and surface-bound enzyme. Urease generates ammonia to buffer gastric acid, promoting gastritis and ulcers; urease-negative mutants fail to infect.​

• Accessory proteins (UreD, E, F, G) activate urease by incorporating Ni²⁺ ions.

• Clinical detection via urease breath test confirms H. pylori infection.​

Absence in Model Organisms

Caenorhabditis elegans and Drosophila melanogaster lack urease. C. elegans handles nitrogen via other pathways, while Drosophila uses urate oxidase for purine catabolism. Humans excrete urea intact, relying on microbial ureases in the gut.​

CSIR NET Relevance

For CSIR NET Life Sciences, recognize Helicobacter pylori as the urease-expressing organism among options. Questions test enzyme distribution, virulence factors, and microbial metabolism.