Which reactive species is produced by myeloperoxidase in neutrophils using hydrogen peroxide and chloride ions?

• A. Hydrogen peroxide
• B. Nitric oxide
• C. Hypochlorous acid (HOCl)
• D. Ozone

Answer: (C)

The main concept is how the neutrophil uses its oxidative enzymes to convert a simple reactive molecule into a powerful antimicrobial agent. In the neutrophil, the respiratory burst generates hydrogen peroxide, and the enzyme myeloperoxidase uses that hydrogen peroxide together with chloride ions to form hypochlorous acid. Hypochlorous acid is a very strong oxidant that kills microbes by damaging proteins, lipids, and DNA, helping to destroy engulfed bacteria. It can also react with amines to form chloramines, boosting antimicrobial activity. Hydrogen peroxide is the substrate in this reaction, not the product; nitric oxide is produced by different cellular pathways, and ozone is not produced by human neutrophils.