Protein concentration using the Lowry Protein Assay.
Protein Determination by the Lowry Assay
The Lowry protein assay method for protein concentration determination is one of the most venerable and widely-used protein assays. The Lowry method was first described in 1951 by Lowry et al. (Lowry et al.,1951).
Hydrolysis is probably the most accurate method of determining protein concentration; followed by amino acid analysis. Most other methods are sensitive to the
amino acid composition of the protein, and absolute concentrations cannot be obtained. The Lowry procedure is sensitive, and is moderately constant from protein to protein. The Lowry protein estimation has been so widely used that it is a completely acceptable alternative to a rigorous absolute determination in almost all circumstances in which protein mixtures or crude extracts are involved.
The method is based on both the Biuret reaction, in which the peptide bonds of proteins react with copper under alkaline conditions to produce Cu+, which reacts with
the Folin reagent, and the Folin–Ciocalteau reaction, which is poorly understood but in essence phosphomolybdotungstate is reduced to heteropolymolybdenum blue by the copper-catalyzed oxidation of aromatic amino acids. The reactions result in a strong blue color, which depends partly on the tyrosine and tryptophan content. The method is sensitive down to about 0.01 mg of protein/mL, and is best used on solutions with concentrations in the range 0.01–1.0 mg/mL of protein.
Chemicals and Substances that Interfere with the Lowry Assay
The Lowry method for protein concentration determination is widely used, however can be subject to interference by many substances and chemicals.
Chemicals that are known to interefere with the Lowry Assay:
- Cesium Chloride
- Nonidet P-40
- Polyvinyl pyrrolidone
- Sodium Deoxycholate
- Sodium Salicylate
- Triton X-100
Lowry Method References
Lowry et al. J. Biol. Chem. 193: 265-275 (1951)