Acid Phosphatase (AP)
Definition
An enzyme present at high concentrations in seminal plasma. The Brentamine Fast Violet B (or SERI AP) spray test detects acid phosphatase activity and is used as a presumptive test for semen. The colour change from colourless to purple indicates AP activity; a result within 30 seconds is considered positive.
- Concentration in semen vs other fluids
- 400 to 500 times higher in semen
- Optimal pH
- Around pH 5 (acidic)
- Common screening test
- Brentamine Fast Blue B (produces purple color)
Common questions
What is acid phosphatase and where is it found?+
Acid phosphatase (AP) is an enzyme present in many body fluids, but semen contains it at exceptionally high concentrations. The prostatic form (PAP) is concentrated in seminal plasma, making it a reliable forensic marker for semen identification.
How is AP used in forensic testing?+
AP serves as a presumptive screening test for semen. The most common method is Brentamine Fast Blue B, which produces a purple color within seconds if AP is detected. This rapid result helps narrow down samples early in forensic analysis.
Why is AP found so much higher in semen than other fluids?+
AP is a phosphomonoesterase enzyme that works best at acid pH levels. The prostatic isoform is uniquely abundant in seminal plasma, with concentrations 400 to 500 times higher than in any other body fluid, which is why it is such a specific and reliable screening marker.
Related terms
- Alpha-Amylase
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- Amylase
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- Barberio Test
- Presumptive semen test. Saturated picric acid reacts with spermine to form yellow rhombic spermine picrate crystals.
- Brentamine Fast Violet B Test
- A two-component spot test in which sodium alpha-naphthyl phosphate (substrate) is hydrolysed by AP to alpha-naphthol, which couples with fast violet B...
- 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...
- Florence Test
- Presumptive semen test. Iodine plus potassium iodide reacts with choline in semen to form dark-brown rhombic / needle-shaped choline iodide crystals.
- Fluorescent AP Assay
- A more sensitive format using 4-methylumbelliferyl phosphate (4-MUP) as substrate. AP cleaves 4-MUP to 4-methylumbelliferone, which fluoresces under UV. Useful on aged...
- Hp, Gc, Tf
- The classical serum-protein polymorphism panel: haptoglobin (binds free haemoglobin; Hp1-1, Hp2-1, Hp2-2 phenotypes), group-specific component (vitamin D binding protein, Gc1F / Gc1S...
- Isoenzyme / Polymorphism
- Different molecular forms of the same enzyme separable by electrophoresis. Forensic polymorphic markers have several common alleles in the population, so a...
- Luminol
- A chemiluminescent reagent (5-amino-2,3-dihydro-1,4-phthalazinedione) that produces blue-white light on contact with haemoglobin-derived iron. Detects blood diluted to 1:10,000,000 or more. Used as...
- P30 (PSA)
- Prostate-specific antigen, a glycoprotein secreted by the male prostate gland and present in semen at high concentrations. ELISA or lateral-flow immunochromatographic tests...
Explained in these topics
- Acid Phosphatase Screening for SemenA group of phosphomonoesterase enzymes that catalyse the hydrolysis of phosphate esters at acid pH (optimum around pH 5). Multiple isoenzymes exist; the prosta...
- Biological Sample Screening and Presumptive TestsAn enzyme present at high concentrations in seminal plasma. The Brentamine Fast Violet B (or SERI AP) spray test detects acid phosphatase activity and is used...
- Body Fluids, RBC Enzymes and Serum Proteins of Forensic SignificanceProstatic enzyme present in semen at concentrations up to approximately 400 times higher than in other body fluids. Used as a presumptive screening test (Brent...