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The Lowry protein assay is a biochemical assay for determining the total level of protein in a solution. The total protein concentration is exhibited by a color change of the sample solution in proportion to protein concentration, which can then be measured using colorimetric techniques.

[edit] Mechanism

The method combines the reactions of cupric ions with the peptide bonds under alkaline conditions (the Biuret test) with the oxidation of aromatic protein residues. The Lowry method is best used with protein concentrations of 0.01-1.0 mg/mL. and is based on the reaction of Cu⁺, produced by the oxidation of peptide bonds, with Folin-Ciocalteu reagent (a mixture of phosphotungstric acid and phosphomolybdic acid in phenol) in the Folin-Ciocalteu reaction. The reaction mechanism is not well understood, but involves reduction of the Folin reagent and oxidation of aromatic residues (mainly tryptophan, also tyrosine). The concentration of the reduced Folin reagent is measured by absorbance at 750 nm^[1]. As a result, the total concentration of protein in the sample can be deduced from the concentration of Trp and Tyr residues that reduce the Folin reagent.

The disadvantage of this method is the long incubation time and there are often interferences with commonly used buffers. This method is also subject to protein-to-protein variation due to the correlation of colour intensity dependent on the content of tyrosine and tryptophan in the protein.

The method was first proposed by Lowry in 1951. The Bicinchoninic acid assay and the Hartree-Lowry assay are subsequent modifications of the original Lowry procedure.

procedure

1.

[edit] References