Fig 3.

Time course of urease activation of H. pylori. H. pylori wild-type and ΔarsS strains were incubated in BHI medium at pH 5.5 or 7.4 for 30 to 180 min, and the total urease activity was measured in the presence of the nonionic detergent C₁₂E₈ to bypass UreI. In the wild-type strain, there was a >3-fold increase in the level of urease activity at pH 5.5 compared to that at pH 7.4 after 30 min, and it remained elevated for 3 h. The absence of ArsS had no effect on urease activity at pH 7.4 but delayed the increase in the urease activity level at an acidic pH seen with the wild-type strain. Activity approached wild-type levels after 180 min (n = 3) (means ± standard errors of the means) (∗, P < 0.05 by t test).