View source for Quantification by Absorbance at 280nm

This method is most accurate with highly purified proteins.

#Using nanodrop measure absorbance in triplicate, ensuring to blank against an appropriate buffer.
#Calculate extinction coefficient for protein of interest
:#Use the [http://www.expasy.ch/tools/protparam.html Protparam] tool to calculate the extinction coefficient in both molar and mg/mL for protein.  Assume all Cys residues are half-cysteines.
:#If the protein is a GST-fusion add 43110 M<sup>-1</sup> and 1.607 mg/mL<sup>-1</sup> respectively
#Divide the absorbance value (normalized by dilution factor if necessary) by the extinction coefficient
#If necessary adjust by the percent purity as described in [[Determining Percent Purity]]