KB03004 | Lowry Protein Quantification Assay

Lowry Protein Quantification Assay is based on Lowry method, first described in 1951. The method relies on two different reactions. The first is the formation of a copper ion complex with amide bonds, forming reduced copper in alkaline solutions. This is called a Biuret chromophore and is commonly stabilized by the addition of tartrate. The second reaction is the reduction of Folin-Ciocalteu reagent (phosphomolybdate and phosphotungstate), primarily by the reduced copper-amide bond complex as well as by tyrosine, tryptophan, histidine, cysteine, and cysteine residues in the protein. The monovalent copper ion catalyzes the latter reaction.
The reduced Folin-Ciocalteu reagent is blue and thus detectable with a spectrophotometer in the range of 500 to 750 nm. The Biuret reaction itself is not very sensitive. Using the Folin-Ciocalteu reagent to detect reduced copper makes the Lowry assay nearly 100 times more sensitive than the Biuret reaction alone.