a bacterial species frequently associated with disease periodontal sites, is known to possess trypsin-like activity. The present study was undertaken to determine the major characteristics of this activity. The trypsin-like activity was mainly found on the surface of the bacteria and could be solubilized with a zwitterionic detergent (Zwittergent 3-14). Using -α-benzoyl-DL-arginine--nitroanilide as substrate, the optimum pH was between 7·5 and 8·5 and the optimum temperature was 35°C. The evidence suggests that the enzyme is a serine protease since it was strongly inhibited by diisopropylfluorophosphate (DFP), -α--tosyl-L-lysine chloromethyl ketone hydrochloride, leupeptin and antipain. The trypsin-like enzyme cleaved numerous chromogenic synthetic peptides containing either an arginine or lysine bond, but could not hydrolyse native proteins including casein, gelatin and BSA. Incubation of a cell envelope extract of the presence of [H]DFP, which is known to bind irreversibly to serine proteases, labelled two bands at 70 and 81 kDa following SDS-PAGE (under reducing conditions) and fluorography. It is suggested that the trypsin-like enzyme may be mainly involved in the degradation of small peptides resulting from hydrolysis of larger proteins by other oral bacteria.


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