Which dye-binding reagent is used for total protein measurement?

• A. Coomassie Brilliant Blue
• B. Methyl Orange
• C. HABA
• D. Benzalkonium chloride

Answer: (A)

The concept here is using a dye that binds to proteins to produce a measurable color change for total protein quantification. The standard dye-binding reagent for this purpose is Coomassie Brilliant Blue G-250, used in the Bradford assay. When the dye binds to proteins, it shifts from a reddish form to a blue form, and the intensity of that blue color increases with protein concentration. Measuring this absorbance, typically around 595 nm, provides a quick estimate of total protein in the sample. This method is popular because it’s simple, fast, and works with many common buffers, though it can be affected by detergents or very high salt. The other substances listed aren’t used for dye-binding protein measurement: one is just a pH indicator, another binds specifically to avidin in biotin assays, and the last is a detergent rather than a dye-binding reagent.