Formation of cyanogen iodide by lactoperoxidase

Area of Science:

• Biochemistry
• Enzymology
• Microbiology

Background:

• Lactoperoxidase (LPO) is a key component of innate immunity in secretions.
• LPO utilizes hydrogen peroxide to oxidize thiocyanate (SCN-) and iodide (I-) into antimicrobial compounds.
• LPO is also used as a preservative in food, oral care, and cosmetic products.

Purpose of the Study:

• To investigate the reaction products of LPO in the presence of both thiocyanate and iodide.
• To identify and characterize the formation of cyanogen iodide (ICN) by LPO.
• To assess the potential relevance of ICN formation in physiological and product contexts.

Main Methods:

• Lactoperoxidase-hydrogen peroxide system with thiocyanate and iodide.
• (13)C nuclear magnetic resonance spectroscopy for product identification.
• Gas chromatography-mass spectrometry for structural elucidation of cyanogen iodide (ICN).

Main Results:

• The inter(pseudo)halogen cyanogen iodide (ICN) was identified as a product of LPO activity when both SCN- and I- were present.
• ICN formation was confirmed using (13)C NMR and GC-MS, particularly when iodide was in slight excess.
• The reaction mechanism involves oxidized iodine species reacting with thiocyanate.
• ICN is also formed by myeloperoxidase and in enzyme-free systems, albeit in lower amounts.

Conclusions:

• Lactoperoxidase catalyzes the formation of cyanogen iodide (ICN) from thiocyanate and iodide.
• ICN formation is unlikely in physiological secretions due to non-competitive conditions for I- and SCN-.
• The formation of ICN may be relevant for LPO-containing products, influencing their preservative or antimicrobial efficacy.