Strategic Planning Colorimetric Protein Assays

The four colorimetric methods for the detection and quantitation presented in this unit have withstood the test of time. They are all well-characterized robust assays that consistently work well. The methods were introduced over the past 15 to 50 years. They collectively represent the state of the art for colorimetric detection and quantitation of total proteins in the microgram to milligram range.

When confronted with the need to determine the total protein concentration of a sample, one of the first issues to consider is selection of a protein assay method. The choice among the available protein assays usually is made based upon consideration of the compatibility of the method with the samples to be assayed. The objective is to select a method that requires the least manipulation or pretreatment of the samples due to the presence of substances that may interfere. If the total protein concentration in the samples is high (i.e., in the range of 5 to 160 mg/ml), the biuret total protein reagent is the best choice. If the total protein concentration in the samples is low (i.e., in the range of 1 to 2000 ^g/ml), then any one of the other three (i.e., the Lowry, the Coomassie plus, or the BCA method) would be suitable. If the sample contains reducing agents or copper-chelating reagents, the Coomassie Plus Protein Assay Reagent (Pierce) would be the best choice. If the sample contains one or more detergents (at concentrations up to 5%), the BCA protein assay reagent is the best choice.

Sometimes the sample contains substances that make it incompatible with any of the protein assay methods. In those cases, some pretreatment of the sample is necessary.

Each method has its advantages and disadvantages. No one method can be considered to be the ideal or best protein assay method. Because of this, most researchers keep more than one type of protein assay reagent available in their lab.

Measurement of Protein Content

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