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Peptide assimilation by Helicobacter pylori was investigated using L-phenylalanyl-3-thia-phenylalanine (PSP) as a detector peptide; the release of thiophenol upon enzymatic hydrolysis of PSP was spectrophotometrically detected with the aid of 5,5’-dithiobis[2-nitrobenzoic acid] (DTNB). By adding PSP to whole-cell suspension, thiophenol was produced progressively, resembling that found in Esherichia coli or Staphylococcus aureus. Interestingly, the rate of thiophenol production by H. pylori in particular was markedly reduced when cells were pretreated with trypsin, indicating surface exhibition of peptidase. According to the competitive spectrophotometry using alanyl-peptides H. pylori did not appear to assimilate PSP through the peptide, transport system. No discernible PSP assimilation could be ascertained in H. pylori cells, unless provided with some additives necessary for peptidase activity, such as Ni2+ or Mg2+ and an appropriate concentration of potassium or ammonium salts. These observations strongly suggest that, regardless of a presumptive peptide transport system, peptide assimilation of H. plori appears to be highly dependent upon milieu conditions, due to unique peptidase exhibition on the cell surface.
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