The
Lowry protein assay is a
biochemicalBiochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
assayAn assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
for determining the total level of
proteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
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
colorimetricColorimetry is "the science and technology used to quantify and describe physically the human color perception."It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE 1931 XYZ color space...
techniques. It is named for the biochemist
Oliver H. LowryOliver Howe Lowry was an American biochemist. He is best remembered for devising the Lowry protein assay.Lowry was the youngest of a family of five children. His father was a teacher and later an administrator in the Chicago public school system...
who developed the technique in the 1940s. His 1951 paper describing the technique is one of the most-highly cited papers ever in the scientific literature, cited over 200,000 times.
Mechanism
The method combines the reactions of copper ions with the
peptide bondThis article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...
s under alkaline conditions (the
Biuret testThe biuret test is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper ion forms a violet-colored complex in an alkaline solution...
) with the oxidation of aromatic
proteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
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 reagentThe Folin–Ciocalteu reagent or Folin's phenol reagent or Folin–Denis reagent, also called the Gallic Acid Equivalence method , is a mixture of phosphomolybdate and phosphotungstate used for the colorimetric assay of phenolic and polyphenolic antioxidants...
(a mixture of
phosphotungstic acidPhosphotungstic acid , tungstophosphoric acid , is a heteropoly acid with the chemical formula 31240. It normally present as a hydrate. EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly...
and
phosphomolybdic acidPhosphomolybdic acid, also known as dodeca molybdophosphoric acid or PMA is a component of Masson's trichrome stain. It is a yellow-green compound, freely soluble in water and polar organic solvents such as ethanol...
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
tryptophanTryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
, also
tyrosineTyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
). The concentration of the reduced Folin reagent is measured by
absorbance at 750 nm. 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 method was first proposed by Lowry in 1951. The
Bicinchoninic acid assayThe bicinchoninic acid assay , also known as the Smith assay, after its inventor, Paul K. Smith at the Pierce Chemical Company, is a biochemical assay for determining the total level of protein in a solution , similar to Lowry protein assay, Bradford protein assay or biuret reagent...
and the Hartree-Lowry assay are subsequent modifications of the original Lowry procedure.
See also
- Biuret test
The biuret test is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper ion forms a violet-colored complex in an alkaline solution...
- another method for estimating the concentration of protein in a solution
External links