Biology Reference
In-Depth Information
result [35]. The presence of SAP is tested for by its ability to catalyse the hydrolysis
of organic phosphate, for example α -naphthyl phosphate, which following hydrolysis
will react with Brentamine Fast Blue (a diazonium salt chromogen), leading to a
colour change [22]. Other biological material containing acid phosphatases can lead
to false positives, such as plant material and vaginal secretions, although the reaction
with semen is usually stronger, and therefore the colour change faster, than with other
material. SAP is quick, simple and safe to perform. As it is an enzyme-based test,
old stains may give a slower reaction, and therefore a longer colour change, and in
some case no reaction may occur if the enzyme no longer functions.
Confirmatory tests
The most commonly used confirmatory test for semen is visualization of the
spermatozoa following staining; commonly used dyes are haematoxylin and eosin
(Figure 3.2b) and Christmas tree stain, which stains heads red and tails green [36].
Another marker for the identification of semen is the protein P30, which is a
prostate-specific antigen (PSA) [37, 38]. The advantage of using PSA compared with
the reaction involving acid phosphatase is that PSA is produced independently from
the generation of sperm and therefore it can be used for both spermic and azoospermic
samples; it is also very sensitive and resistant to degradation, even in cadavers [39].
Detection of PSA is most common with the use of the immunochromatographic strip
test, using antibodies raised against human PSA [40 - 42] (Figure 3.6).
Another confirmatory test is mRNA analysis, detecting the semen-specific pro-
tamine (PRM)1, PRM2 and kallikrein 3 (PSA) genes [24, 28, 29].
Saliva
Saliva is a fluid produced in the mouth to aid in swallowing and the initial stage of
digestion. A healthy person produces between 1 L and 1.5 L of saliva every day and
can transfer saliva, along with epithelial cells sloughed off from the buccal cavity,
in a number of ways. Transfer may be by contact, such as on food products when
eating, drinking vessels, cigarette butts, envelopes or in oral sexual assaults. Transfer
may also be by aerial deposition of saliva such as on to the front of a mask when
worn over the head or on to a telephone when talking into the mouthpiece.
Presumptive tests
As with blood and semen ALS can be used to locate saliva; stains appear blue-white
when viewed under UV light. Most presumptive tests for saliva make use of the
enzyme α -amylase, which is present at high concentrations and digests starch and
complex sugars. The
1 - 4 glycosidic bonds in glu-
cose polymers, such as glycogen and starch. The digestion of starch can be assessed
using the starch - iodine test: a sample of the evidential stain is incubated with a
α
-amylase enzyme hydrolyses
α
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