SYNTHESIS AND ACTIVITY OF HELICOBACTER-PYLORI UREASE AND CATALASE AT LOW PH

Background-Helicobacter pylori produces large amounts of urease presum ably to be prepared for the rare event of a sudden acid exposure. The hypothesis that H pylori is acid sensitive and protein production is i nhibited by low pH was examined. Methods-H pylori or its soluble enzym es were incubated buffered or unbuffered at a pH ranging from 2-7 in t he presence of 5 mM. urea for 30 minutes. After exposure, urease and c atalase activities of whole cells, supernatants, and soluble enzyme pr eparations were measured at pH 6.8. Newly synthesised enzyme was quant ified by immunoprecipitation of [S-35]-methionine labelled protein. Re sults-Exposure to buffer below pH 4 resulted in loss of intracellular urease activity. In soluble enzyme preparations and supernatant, no ur ease activity was measurable after incubation at pH<5. In contrast, ca talase in whole cells, supernatant, and soluble enzyme preparations re mained active after exposure to pH greater than or equal to 3. Exposur e below pH 5 inhibited synthesis of total protein including nascent ur ease and catalase. At pH 6 or 7, urease represented 10% of total prote in, catalase 1.5%. Exposure of H pylori to unbuffered HCl (pH>2) resul ted in an immediate neutralisation; urease and catalase activities and synthesis were unchanged. Conclusion-Low surrounding pH reduces activ ity of urease and synthesis of nascent urease, catalase, and presumabl y of most other proteins. This suggests that H pylori is not acidophil ic although it tolerates short-term exposure to low pH.