de Koning-Ward T F, Robins-Browne R M
Department of Microbiology and Infectious Diseases, Royal Children's Hospital, Parkville, Victoria, Australia.
FEMS Microbiol Lett. 1997 Feb 15;147(2):221-6. doi: 10.1111/j.1574-6968.1997.tb10245.x.
Yersinia enterocolitica produces the enzyme urease which hydrolyses urea, resulting in the production of carbonic acid and ammonia and a net increase in pH. In the presence of urea, urease enhances survival of Y. enterocolitica in the stomach and presumably in other acidic environments the bacteria encounter during the course of infection. In this study we show that Y. enterocolitica urease is a cytosolic enzyme which has a low Km value (0.15 +/- 0.01 mM urea), suggesting that it functions at close to maximum velocity even at the low concentrations of urea available to Y. enterocolitica in gastric fluid and other tissues. Y. enterocolitica urease was active over a wide pH range, but unlike most other bacterial ureases, displayed an optimal activity at pH 3.5-4.5, suggesting a physiological role in protecting the bacteria from acid. Higher levels of urease activity were attained at 28 degrees C than at 37 degrees C, and investigation of the regulation of urease production revealed that the enzyme was not induced by urea, or by nitrogen limitation. Instead maximal activity was attained during the stationary phase of growth which coincides with the period of maximum acid tolerance of the bacteria. This type of regulation has not been described for any other ureolytic bacteria and seems to be unique to Y. enterocolitica.
小肠结肠炎耶尔森菌产生尿素酶，该酶可水解尿素，生成碳酸和氨，使pH值净增加。在有尿素存在的情况下，尿素酶可提高小肠结肠炎耶尔森菌在胃中的存活率，并且推测在感染过程中细菌遇到的其他酸性环境中也能提高其存活率。在本研究中，我们表明小肠结肠炎耶尔森菌尿素酶是一种胞质酶，其米氏常数（Km值）较低（0.15±0.01 mM尿素），这表明即使在胃液和其他组织中小肠结肠炎耶尔森菌可利用的尿素浓度较低时，它也能以接近最大速度发挥作用。小肠结肠炎耶尔森菌尿素酶在较宽的pH范围内都有活性，但与大多数其他细菌尿素酶不同的是，它在pH 3.5 - 4.5时表现出最佳活性，这表明其在保护细菌免受酸侵害方面具有生理作用。在28℃时获得的尿素酶活性水平高于37℃，对尿素酶产生的调控研究表明，该酶不是由尿素或氮限制诱导产生的。相反，最大活性是在细菌生长的稳定期达到的，这与细菌最大耐酸性的时期相吻合。这种调控类型在其他尿素分解细菌中尚未有描述，似乎是小肠结肠炎耶尔森菌所特有的。
