Figure 7.

Hypochlorous acid (HOCl) inhibits bradykinin production. A: The proteolytic activity of kallikrein is abolished by HOCl dose-dependently but is protected when HOCl is quenched with l-methionine (20-fold molar excess). Shown are the results (with SDs) of three separate experiments. B: HK is oxidized by HOCl, resulting in a product uncleavable by active kallikrein. HK was pretreated with increasing concentrations of HOCl. A 20-fold excess of l-methionine was added (20 minutes) before the addition of active kallikrein. Bradykinin production was assessed by ELISA. Shown are the results from four separate experiments. C: HOCl inactivates kininogen by oxidizing a critical methionine residue. HOCl-oxidized HK was treated with a methionine sulfoxide reductase (PilB), and the inhibition of bradykinin production was reversed. DTT, dithiothreitol.