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Pierce 660 nm Protein Assay FAQ

Answers to frequently asked questions (FAQs) about Pierce 660 nm Protein Assay Reagent and Kit


How does the Pierce 660 nm Protein Assay Kit work?
The assay is based on a dye-metal complex that binds to proteins in an acidic solution. Upon binding, the reddish dye-metal complex changes to green, resulting in an absorbance shift measurable at 660 nm. The dye interacts mainly with basic residues, such as histidine, arginine and lysine and to a lesser extent, tyrosine, tryptophan and phenylalanine.

What formats are available for the Pierce 660 nm Protein Assay?
There are two formats: The complete kit (#22662) contains sufficient reagents for 300 test tube or 3,000 microplate assays and a set of pre-diluted BSA standards with concentrations from 125 to 2,000 mg/ml. The assay reagent (750 ml, #22660) is sufficient for 500 test tube or 5,000 microplate assays.

What advantages does the Pierce 660 nm Protein Assay have over other protein assays?
The Pierce 660 nm Protein Assay has the following advantages:

  • Room temperature stability of the assay reagent
  • A greater linear range than the coomassie-based Bradford assays
  • Compatibility with commonly used detergents and reducing agents
  • Compatibility with samples lysed in Laemmli sample buffer
  • Rapid mix-and-read protocol

Can I measure the absorbance at a wavelength other than 660 nm?
If a 660 nm filter is not available, the assay can be measured at wavelengths from 645 to 670 nm; however, the assay linear range is 25-2,000 µg/ml and occurs only when the absorbance of the dye-protein complex is measured at 660 nm. Measuring the absorbance at wavelengths other than 660 nm will result in a decrease of the assay?s linear range and might increase the minimum detection level (i.e., decrease sensitivity).

What is the linear range of the Pierce 660 nm Protein Assay?
The assay?s linear range is 25-2,000 µg/ml using the test tube procedure and 50-2,000 µg/ml using the microplate procedure.

Can I use the Pierce 660 nm Protein Assay to quantify peptides?
The Pierce 660 nm Protein Assay can quantify peptides that are at least 2,500 Da if their compositions include amino acid residues that react with the dye-metal reagent (i.e., histidine, arginine, tyrosine, tryptophan and phenylalanine). For peptides smaller than 2,500 Da, use the Fluoraldehyde Reagent Solution (#26025), which detects amino groups.


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