protein analysis by liquid phase colorimetry with spectrophotometric readout bicinchoninic acid protein assay 2013-11-12T17:03:03Z BCA protein assay JSmith MMO:0000424 The BCA protein assay combines the protein-induced biuret reaction in which peptide bonds in the protein reduce Cu2+ ions to Cu+ in a reaction proportional to the amount of protein present, followed by chelation of bicinchoninic acid molecules with Cu+ ions, forming a purple-colored product which can be quantitated by spectrophotometry, i.e., based on the ability of the solution to alter the transmission of light at specific wavelengths in the visible spectrum, that is, to alter the transmission of a specific color of light. measurement_method_ontology