P 008 - Formation of cyanogen iodide by heme peroxidases

Abstract

The heme-containing proteins lactoperoxidase (LPO) and myeloperoxidase are important enzymes involved in immune defence reactions. They are well known for their ability to oxidise in a hydrogen peroxide-driven reaction thiocyanate, iodide and in case of myeloperoxidase also bromide and chloride to the corresponding hypo(pseudo)halous acids. Here we describe the formation of cyanogen iodide (ICN) as a novel product of these enzymes. The formation of ICN was evidenced by both 13 C-nuclear magnetic resonance spectroscopy by applying 13 C-labeled thiocyanate and by head-space gas-chromatography mass spectrometry. This product is only formed when iodide is used in excess over thiocyanate during these reactions. Furthermore, the formation of bactericidal components by the LPO-hydrogen peroxide-thiocyanate/iodide system was investigated on a luminescent E. coli strain. This approach delivered time-resolved data about the killing of these microorganisms. In the mixed presence of thiocyanate and iodide (with an excess of iodide) a considerably higher killing rate was observed than in the sole application of either ion species. These data correspond well with the direct apllication of ICN. Control experiments of the determination of colony-forming units confirmed the results. Our data offer a novel product pathway that may be important for numerous biotechnological application of LPO.