Which of the following methods will give you a measure of yo

Which of the following methods will give you a measure of your protein concentration when your protein sample is ~50% pure.

Lowry assay

Bradford assay

Spectrophotometric assay

BCA assay

None of the agove

Solution

When the protein sample is ~50% pure, the best method of anaysing its concentration is BRADFORD assay. Bradford assay relies on the formation of a complex between Coomassie brilliant blue G-250 dye and proteins in solution. Free dye exists in 4 different ioninc forms and most anioninc form binds to protein and show absorbance in spectrophotometer at 590nm. Protein concentration can be evaluated by determining the amount of dye in blue ioninc form ehich binds mostly with arginine, tryptophan, tyrosine, histidine and phenylalanine residues.

As the sample is ~50% pure, that means it contains some amount of other materials like salt, solvents, buffers, metals, chelating agents and some reducing agents to stabilize the protein. the advantage of Bradford method is its compatibility with these materials and these materials does not interfere with the process, where as these are not compatible with Lowry assay and to some extent BCA assay.

In a recent paper describing protein assay and recovery, Cheng et al described Bradford assay-based method for rapid protein quantification even the protein soluiton contains interfering substances.