Dominance of iminopeptidase activity in the human oral bacterium Treponema denticola ATCC 35405

Abstract

Treponema denticola ATCC 35405, a human oral spirochete associated with periodontal disease, was shown to contain three enzymes (I, II, and III) with proline iminopeptidase activity. II and III were considered to be true iminopeptidases, whereas enzyme I was found to be a benzoylarginine peptidase with iminopeptidase activity. Enzyme III, the dominant proline iminopeptidase of T. denticola in terms of its activity toward N - l -prolyl-2-naphthylamine, was considered to be a sulfhydryl peptidase: 0.167 μ M p -chloromercuribenzoic acid totally inactivated the enzyme, and 1.0 m M dithiothreitol restored 92% of activity. The activity of this enzyme was not affected by metal chelators. Chemical modification of enzyme III suggests that tyrosyl (or histidyl) and carboxyl groups may be necessary for its activity. The hydrolysis of N - l -prolyl-2-naphthylamine was found to be very characteristic of T. denticola ATCC 35405; out of 24 different N - l -aminoacyl-2-naphthylamines tested, only the proline derivative was hydrolyzed at a high rate. The substrate specificity of the enzymes discovered indicates that they may be important for the nutrition of T. denticola . The iminopeptidase activity may be related to the pathogenicity of this organism in periodontal disease.