Fig. 2.

Trp/Cl⁻ inhibit H₂O₂ consumption by MPO. (Panel A) A typical recording by an H₂O₂-selective electrode demonstrating the autoreduction of H₂O₂ (20 μM) following addition to a stirred 0.2 M phosphate buffer (pH 7.0) supplemented with 100 mM Cl⁻, at 25 °C (dashed line). Addition of 20 μl (20 nm in 3ml solution, final) of MPO solution to the H₂O₂/Cl⁻ stirred buffer caused rapid H₂O₂ consumption (dotted line). Addition of 20 μl (30 nM final) MPO solution to the H₂O₂/Cl⁻ solution supplemented with increasing Trp concentrations 5, 7, 14, 28, 60 and 100 μM (solid lines from left to right, respectively) causing slower H₂O₂ removal. (Panel B) Similar reactions were repeated by adding 20 μl (200 nM) MPO to the H₂O₂/Cl⁻ solution supplemented with increasing Trp concentrations (60, 100, 400, 800, 1600 μM, sold lines, left to right, respectively). Tracings shown are from a typical experiment performed at least three times.