Practice question

Survival in strongly acidic niches such as stomach lumen colonized by Helicobacter pylori causing gastritis and ulcer disease requires exceptionally efficient neutralization of extreme acidity. Urease is extraordinarily active nickel-dependent metalloenzyme encoded by ureABIEFGH operon containing structural subunits UreA and UreB plus accessory proteins UreE, UreF, UreG, UreD for nickel insertion, hydrolyzing urea abundant in gastric juice and urine into two molecules of ammonia and one carbon dioxide. Ammonia immediately protonates to ammonium NH4+ consuming protons and raising local pH from about 2 to near neutrality, creating protective alkaline cloud that prevents acid denaturation of periplasmic and surface proteins. Carbon dioxide hydrates via carbonic anhydrase to bicarbonate adding second buffering layer. In H. pylori urease represents up to 10 percent total cellular protein. It does not aid protein folding like chaperone nor degrade antibiotics like beta-lactamase nor block glycolysis; its chemical product directly elevates pH and simultaneously provides nitrogen assimilation pathway via glutamine synthetase, underpinning colonization success and pathogenesis.