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Section 11-Protein Lowry
11. Protein Lowry
The Modified Lowry Protein Assay is an alternative method for
determining protein concentration based on the widely used and cited
Lowry procedure for protein quantitation. Like the BCA and Bradford
Assays, the Modified Lowry Assay requires standard curve generation
each time it is run, before unknown proteins can be measured. The
Modified Lowry procedure involves reaction of protein with cupric
sulfate in alkaline solution, resulting in formation of tetradentate
copper-protein complexes. The Folin-Ciocalteu Reagent is effectively
reduced in proportion to the chelated copper-complexes resulting in a
water-soluble blue product that is measured at 650 nm and
normalized at 405 nm. Pre-formulated reagents, 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 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
The Modified Lowry assay concentration range of detection is ~0.20
mg/ml to 8.0 mg/ml (BSA) on the NanoDrop 8000.
11-1
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