What is the role of peroxidases in the Kastle-Meyer test?

• A. They inhibit oxidation to prevent false positives.
• B. They are not involved; color change is due to hemoglobin only.
• C. They accelerate the oxidation of organic compounds through peroxides.
• D. They color the solution blue regardless of sample.

Answer: (C)

Hemoglobin in blood provides peroxidase-like activity, acting as the catalyst in a peroxide-driven oxidation. This peroxidase activity speeds up the oxidation of the indicator (phenolphthalein) by hydrogen peroxide, producing the characteristic pink color when blood is present. Without this catalytic action, hydrogen peroxide alone would not generate the rapid, visible color change. So, the role of peroxidases here is to accelerate the oxidation of organic compounds through peroxides, enabling the pink reaction to indicate blood. The other ideas—inhibiting oxidation, having no involvement, or coloring blue—do not fit the actual mechanism or the observed color change of Kastle-Meyer.