What is Lowry assay?
The Lowry 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 according to the protein concentration of sample solution, which can then be measured using colorimetric techniques. It is named for the biochemist Oliver H. Lowry who developed the reagent and used it. Lowry assay is one of the colorimetric methods which may be more sensitive for determine total protein concentrations nonspecifically. In generally, this technique is based on an absorbance signal proportional to the protein concentration.
What is the principle of Lowry assay?
The exact mechanism of colorimetric assay in the Lowry assay remains in two distinct steps. First, protein is reacted with divalent copper ion forms under alkaline conditions. During this incubation, the copper forms a complex with peptide binds in which it is reduced to a monovalent ion. Second, Folin-phenol reagent (the phosphomolybdic-phosphotungstic acid solution) is added the solution. This compound can be reacted with the radical groups of tyrosine, tryptophan and cysteine, producing an intense blue color. It is believed that the color enhancement occurs when the tetradentate copper complex transfers electrons to the Folin-phenol reagent complex. It has been suggested that during the 30 minute incubation, a rearrangement of the initial unstable blue complex leads to the stable final blue colored complex, resulting in an optimal absorbance at 750nm. In addition, it can be measured at wavelength between 650nm and 750nm with little loss of color intensity.
What is Lowry assay used for?
Lowry assay is one of the useful techniques for determine protein concentrations. There are also some other colorimetric assays such as Bradford and BCA in biopharmaceutical.
Common Colorimetric Protein Assay
| Assay Method | Suggested Range | Wavelength Analyzed | Linear Response | Approximate Test Volume |
|---|---|---|---|---|
| Lowry assay | 1-20 μg | 750 nm | Yes | 200 μl |
| Bradford assay | 1-10 μg | 595 nm | No | 200 μl |
| BCA method | 0.5-200 μg | 562 nm | Yes | 200 μl |
* reference see Handbook of Modern Pharmaceutical Analysis, Satinder Ahuja, Stephen Scypinski, 2010.
