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List of methods
Direct absorbance measurementabsorbance at 280 nm Colorimetric assaysset up an assay |
Quantifying protein using absorbance at 205 nmConsiderations for useSee considerations listed under the absorbance at 280 nm. This method is just as convenient. It may be preferred if there is excessive contamination by nucleic acids, since nucleic acids absorb very little radiation at 205 nm. Setting the wavelength is a bit tricky since 205 nm is right on the shoulder of the protein peak. PrincipleSee the discussion for quantifying protein using absorbance at 280 nm.
EquipmentIn addition to standard liquid handling supplies a spectrophotometer
with UV lamp and quartz cuvette are required.
ProcedureInclude 0.01% Brij 35 in the buffer to prevent adsorption
of protein onto plastic or glass surfaces. This is necessary for measurements at
205 nm because losses are proportionately higher in dilute solutions.
AnalysisProtein concentration (mg/ml) = (Absorbance at 205 nm)/31.
CommentsCold solutions can fog up the cuvette, while warm solutions
can release bubbles and interfere with the readings. Solutions must be
much more dilute than for measurements at 280 nm. Proteins absorb much more strongly
at 205 nm, and there is supposedly less variability from protein to protein.
In addition to the need for an accurate wavelength setting, stray light
can be a major problem. To avoid these problems, use a 10 microgram/microliter
solution of bovine serum albumin as a standard. With buffer blank as
zero absorbance, determine the concentration of an unknown (concentration
between 0 and 10 micrograms/microliter) by interpolation. This is acceptable
because of the linear relationship of absorbance and concentration in
the 0 to 10 microgram/microliter range.
The problem of an accurate wavelength setting can be avoided by determining absorbance at 210 nm (extinction coefficients range from 20 to 24). However there is less sensitivity and more variation with buffer conditions. References
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Copyright
and Intended Use Visitors: to ensure that your message is not mistaken for SPAM, please include the acronym "Bios211" in the subject line of e-mail communications Created by David R. Caprette (caprette@rice.edu), Rice University 24 May 95 Updated 12 Jun 15 |