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Hartree-Lowry and Modified Lowry Protein Assays

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❶The Blue color developed by the reduction of the Phosphomolybdic-Phosphotungastic components in the Folin-ciocalteau reagent by the amino acids Tyrosine and Tryptophan present in the protein plus the color developed by the biuret reaction of the protein with the color developed by the biuret reaction of the protein with the alkaline cupric tartarate are measured in the Lowry method.

Considerations for use

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The preparation of this reagent has been described ; however, the solution can be obtained from commercial sources Sigma. Lowry is not an endpoint assay, so samples should be staggered to obtain more accurate estimates.

The response observed will be linear over a limited range of standards. Polynomial, exponential, and logarithmic models can be used to fit the data to extend the dynamic range of the response curve. The Lowry assay has been largely superseded by the BCA assay due to sensitivity, linearity, and improved methodology. The Lowry protein assay is sensitive to many interfering compounds Table 8.

Formation of precipitates can occur with detergents, lipids, potassium ions, and sodium phosphate. Nuno Borges, in Methods in Microbiology , The Bradford method, the Lowry method and the bicinchoninic acid BCA method, using bovine serum albumin as protein standard, are widely used to measure protein levels.

These are quick colorimetric methods that yield reproducible results Bradford, ; ;. The Bradford method is probably the most popular one since it is rapid, has high sensitivity and very few interferences by nonprotein components.

However, it has the disadvantage of high protein-to-protein variations. This limitation has been overcome in the procedure involving bicinchoninic acid. This is the protein assay currently favored in our laboratory. Pierce Chemical Company Illinois, USA commercializes a kit with standard solutions for this method, which minimizes errors and improves reproducibility. The analyte concentration is determined by the Lowry method, and the number of maleimide groups introduced per molecule is determined as follows.

Two hundred microliters of 0. The protein content of membranes is determined by the Lowry assay 4. To measure low protein concentrations quickly with high sensitivity in purified fractions the Coomassie dye-binding assay according to Bradford 5 is used. For both assays bovine serum albumin fatty acid free is used as a standard.

In separate experiments we determined that the protein contents of solubilized and purified CCDR preparations measured with the Bradford assay are slightly higher 1. This must be taken into account if specific binding activities of particulate and purified receptor preparations are compared. Clementi, in Methods in Neurosciences , Recording of absorbances need only be done within 10 min. This modification is less sensitive to interfering agents and is more sensitive to protein than the original.

As with most assays, the Lowry can be scaled up for larger cuvette sizes, however more protein is consumed. Proteins with an abnormally high or low percentage of tyrosine, tryptophan, or cysteine residues will give high or low errors, respectively. Under alkaline conditions the divalent copper ion forms a complex with peptide bonds in which it is reduced to a monovalent ion. In addition to standard liquid handling supplies a spectrophotometer with infrared lamp and filter is required.

Glass or polystyrene cheap cuvettes may be used. Keeps 2 to 3 months. Reagent C consists of 1 vol Folin-Ciocalteau reagent diluted with 15 vols water. Prepare a series of dilutions of 0.

Incubate the tubes 10 min in a 50 degrees C bath, then cool to room temperature. Rapidly add 3 ml reagent C to each tube, mix, incubate 10 min in the 50 degree bath, and cool to room temperature. Final assay volume is 5 ml. Prepare a standard curve of absorbance versus micrograms protein or vice versa , and determine amounts from the curve.

Dissolve 20 gm sodium carbonate in ml water, 0. Mix all three solutions to prepare the copper reagent. March Learn how and when to remove this template message. Protein Determination by Oliver H. Journal of Biological Chemistry.

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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.

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The Lowry assay () is an often-cited general use protein assay. For some time it was the method of choice for accurate protein determination for cell fractions, chromatography fractions, enzyme preparations, and so on.

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PROTEINS (LOWRY) PROTOCOL 1. INTRODUCTION The “Lowry Assay: Protein by Folin Reaction” (Lowry et al., ) has been the most widely used method to estimate the amount of proteins (already in solution or easily-soluble in dilute alkali) in biological samples. First the proteins are pre-treated with copper ion in alkali solution, and then. Estimation of Proteins by Lowry method: This is the basic laboratory protocol of Protein estimation. Most frequently using hlcss.mltion lab protocols.

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The Lowry method is sensitive to low concentrations of protein. Dunn [] suggests concentrations ranging from - 2 mg of protein per ml while Price [] suggests concentrations of - mg of protein per ml. The major disadvantage of the Lowry method is the narrow pH range within which it is accurate. Learn more about Lowry protein assay. Guide to Protein Purification, 2nd Edition. James E. Noble, Protein Determination. Samples of the cell-loaded support were dried and assayed for protein content according to the Lowry method [10].