FIG. 6.

Schematic representation of the direct and indirect Glu, Gln, Asp, and Asn incorporation pathways associated with ammonia production in H. pylori. H. pylori (top) is represented in contact with a host epithelial cell (bottom). The proteins described in this work are represented by filled circles. At neutral pH, Glu and Asp are transported directly into the cytoplasm. In contrast, Gln and Asn are exclusively taken up by indirect pathways (illustrated by the two crosses). Gln and Asn hydrolysis in the periplasm generates ammonia plus Glu and Asp, respectively. A model is presented in which these two nonredundant systems participate in H. pylori virulence by depleting gastric or immune cells from protective amino acids and producing toxic ammonia in contact with the host cells. Abbreviations: Glu, l-glutamate; Gln, l-glutamine; Asp, l-aspartate; Asn, l-asparagine; NH₃, ammonia; γGT, γ-glutamyltranspeptidase; AnsB, asparaginase.