Introduction
The Bio-Rad Protein Assay, based on the method of Bradford, is a
simple and accurate procedure for determining concentration of solubilized
protein. It involves the addition of an acidic dye to protein solution,
and subsequent measurement at 595 nm with a spectrophotometer or
microplate reader. Comparison to a standard curve provides a relative
measurement of protein concentration.

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http://www.fhcrc.org/science/labs/hahn/methods/biochem_meth/biorad_assay.pdf