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Section 10- Protein BCA
10. Protein BCA
The BCA (Bicinchoninic Acid) Protein Assay is an alternative method
for determining protein concentration. It is often used for more dilute
protein solutions and/or in the presence of components that also have
significant UV (280 nm) absorbance. Unlike the Protein A280 method,
the BCA Assay requires a standard curve to be generated each time it
is run, before unknown proteins can be measured. The resulting Cu-
BCA chelate formed in the presence of protein is measured at its
wavelength maximum of 562 nm and normalized at 750 nm. Pre-
formulated reagents of BCA and CuSO
4
, utilized in the assay, are
available in kit form from numerous manufacturers. Follow their
recommendations when mixing the respective reagents at the time
the assay is to be performed.
Sample Volume Requirements
Some proteins are hydrophobic and others hydrophilic giving rise to
variable surface tension properties in the sample to be measured.
Additionally the presence of surfactants or detergents in reagents,
such as the Bradford reagent, can significantly alter surface tension.
This occurrence can be overcome without affecting the sample’s
absorbance by using a larger sample volume.
A 2 ul sample size is
recommended for protein measurements
.
Pedestal Reconditioning
Solutions and reagents containing surfactants may “un-condition” the
measurement pedestal surfaces so that the liquid column does not
form. If this occurs, “buff” the measurement pedestal surfaces by
rubbing each measurement surface aggressively with a dry laboratory
wipe 30-40 times. This will “re-condition” the surface allowing the
liquid sample column to form. Alternatively, use the NanoDrop
Pedestal Reconditioning Compound (PR-1) as a rapid means of
reconditioning the pedestals when the surface properties have been
compromised and liquid columns break during measurement.
Additional information about the PR-1 kit may be found on our
website.
Measurement Concentration Range
When using a 20:1 reagent to sample volume dilution, the BCA assay
concentration range of detection is ~0.20 mg/ml to 8.0 mg/ml on the
NanoDrop 1000. Using a 1:1 reagent to sample volume dilution the
concentration range of detection is 0.01 mg/ml – 0.20 mg/ml.
10-1