Bacterial lipases are attracting an enormous amount of attention due to their wide biotechnological applications and due to their roles as virulence factors in some bacteria. Helicobacter pylori is a significant and widespread pathogen which produces a lipase(s) and phospholipases that seem to play a role in mucus degradation and the release of proinflammatory and cytotoxic compounds. However, no H. pylori lipase(s) has been isolated and described previously. Therefore, a search for putative lipase-encoding genes was performed by comparing the amino acid sequences of 53 known lipolytic enzymes with the deduced proteome of H. pylori. As a result, we isolated, cloned, purified, and characterized EstV, a novel lipolytic enzyme encoded by open reading frame HP0739 of H. pylori 26695, and classified it in family V of the bacterial lipases. This enzyme has the properties of a small, cell-bound carboxylesterase (EC 3.1.1.1) that is active mostly with short-chain substrates and does not exhibit interfacial activation. EstV is stable and does not require additional cofactors, and the maximum activity occurs at 50 degrees C and pH 10. This unique enzyme is the first lipase isolated from H. pylori that has been described, and it might contribute to ulcer development, as inhibition by two antiulcer substances (beta-aescin and glycyrrhizic acid) suggests. EstV is also the first lipase from an epsilon-proteobacterium to be described. Furthermore, this enzyme is a new member of family V, probably the least-known family of bacterial lipases, and the first lipase of this family for which kinetic behavior, inhibition by natural substances, and other key biochemical features are reported.