Mobley H L
University of Maryland School of Medicine, Baltimore, 21201, USA.
Aliment Pharmacol Ther. 1996 Apr;10 Suppl 1:57-64. doi: 10.1046/j.1365-2036.1996.22164006.x.
Helicobacter pylori produces a 550 kDa, multimeric, nickel-containing urease that catalyses the hydrolysis of urea to yield ammonia and carbonic acid. The ure gene cluster, comprised of seven genes, encodes the two structural subunits UreA (26.5 kDa) and UreB (60.3 kDa), and five accessory proteins: UreI, UreE, UreF, UreG and UreH. Accessory proteins are required for nickel ion insertion into the apoenzyme. The native protein consists of six copies each of UreA and UreB; two nickel ions are coordinated into each UreB active site. Urease is found in the cytosol, but may also localize on the surface (although this may be an artefact) and elicits a strong serum immunoglobulin response. Urease aids in colonization of the host by neutralizing gastric acid and providing ammonia for bacterial protein synthesis. Host defences are avoided by urease by continuing to neutralize acid locally and by shedding urease, which may be bound by immunoglobulin, from the surface of the bacterium. Host tissues can be damaged directly by the urease-mediated generation of ammonia and indirectly by urease-induced stimulation of the inflammatory response, including recruitment of leukocytes and triggering of the oxidative burst in neutrophils.
幽门螺杆菌产生一种550 kDa的多聚体含镍脲酶，该酶催化尿素水解生成氨和碳酸。脲基因簇由七个基因组成，编码两个结构亚基脲酶A（26.5 kDa）和脲酶B（60.3 kDa），以及五个辅助蛋白：脲酶I、脲酶E、脲酶F、脲酶G和脲酶H。辅助蛋白是镍离子插入脱辅基酶所必需的。天然蛋白由脲酶A和脲酶B各六个拷贝组成；两个镍离子配位到每个脲酶B活性位点。脲酶存在于细胞质中，但也可能定位于表面（尽管这可能是一种假象），并引发强烈的血清免疫球蛋白反应。脲酶通过中和胃酸和为细菌蛋白质合成提供氨来帮助在宿主体内定殖。脲酶通过持续在局部中和酸以及从细菌表面释放可能被免疫球蛋白结合的脲酶来逃避宿主防御。宿主组织可被脲酶介导产生的氨直接损伤，也可被脲酶诱导的炎症反应间接损伤，包括白细胞募集和中性粒细胞氧化爆发的触发。
