Streptavidin is a protein that has similar binding
properties to egg white avidin
It is isolated from streptomyces avidinii. Streptavidin has a
molecular weight of 60 KD and has 4 subunits.
Each subunit can bind one molecule of biotin. Biotin is a
watersoluble vitamin.
Streptavidin has an extremely high binding affinity (Kd=10-15) for
biotin. It has proven useful in the detection of antigens coupled with
biotinylated secondary antibodies. There are several advantages when using
streptavidin versus an avidin complex (ABC). In contrast to avidin, streptavidin
is not glycosylated and is therefore uncharged at neutral pH (6.5 versus 10).
This lowers nonspecific background staining.
Streptavidin also lacks carbohydrate side chains that may be
another cause of non-specific background. Another key advantage of streptavidin
is the significant increase in sensitivity (probably due to less steric
hindrance),
thus facilitating an increase in overall binding capacity.
Finally, streptavidin-enzyme conjugates are much more stable than
an ABC complex.
The ABC complex must be freshly made 30 minutes prior to use and
is stable only for a few days. In contrast, a streptavidin-conjugate can be
stored for up to 1-2 years.
The reagent comes in a ready-to-use format, thus saving time and
potential mistakes.BIOCARE’S 4plus™ detection system has been developed to
provide a significant increase in staining sensitivity. The vast majority of
primary antibodies can be diluted two-fold compared to other commercially
available detection systems. 4plus™ Universal Detection system can be used with
both mouse and rabbit primary antibodies.
After labeling the antigen with a primary antibody, a universal,
affinitypurified, biotinylated secondary antibody is added to bind to the
primary antibody. Horseradish peroxidase (HRP) labeled-streptavidin is then
added to bind to the biotinylated secondary antibody.
A chromogen/substrate is then applied and reacts with a specific
enzyme to produce an intense color signal. 4plus™ detection systems work well
with paraffin-embedded tissues, frozen sections and cell
preparations.
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