Peroxidase-Like Activity
Definition
The catalytic behaviour of haemoglobin (and other haem-containing proteins) that mimics the enzyme peroxidase: splitting hydrogen peroxide into water and oxygen. The released oxygen drives the colour reaction.
- Source protein
- Haemoglobin and other haem-containing proteins
- Mimicked enzyme
- Peroxidase
- Reaction
- Splits hydrogen peroxide into water and oxygen
- Test relevance
- Drives the Kastle-Meyer colour change
Common questions
How does the released oxygen actually produce the visible colour in the Kastle-Meyer test?+
The oxygen released from hydrogen peroxide breakdown oxidises the reduced, colourless phenolphthalein reagent back into its pink form, so the colour change is a downstream effect of the peroxidase-like reaction, not a direct blood indicator.
Is a positive Kastle-Meyer result proof the stain is human blood?+
No, it is a presumptive test only. Other peroxidase-like substances, including some plant matter and certain oxidising chemicals, can trigger the same colour change, so confirmatory species and DNA testing follow a positive result.
Why does this activity make presumptive tests useful for screening large scenes?+
Because the reaction is fast, cheap, and sensitive to trace amounts of haem, it lets investigators quickly narrow down which of many stains at a scene are worth collecting for slower, more expensive confirmatory laboratory testing.
Related terms
- Confirmatory Test
- A test with sufficient specificity to establish the identity of a biological fluid for reporting purposes. Examples include Takayama and Teichmann crystal...
- False Positive
- A test result that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
- Haem Group
- The iron-porphyrin prosthetic group at the centre of haemoglobin. The iron atom cycles between oxidation states during the peroxidase-like reaction, and it...
- Leuco-Phenolphthalein
- The reduced, colourless form of phenolphthalein used in the Kastle-Meyer reagent. It is oxidised back to the pink quinone form in the...
- Presumptive Test
- A fast, low-cost, class-specific screen used to triage a caseload before instrumental work begins. Examples are Marquis reagent for opioids and amphetamines,...