The biuret method for determining serum total protein is dependent upon which structural feature of proteins?

The biuret method for determining serum total protein is dependent upon which structural feature of proteins?

• A. Number of Peptide Bonds
• B. Hemoglobin Content
• C. Carbohydrate Chains
• D. Lipid Content

Answer: (A)

Biuret method relies on the presence of peptide bonds in proteins. In alkaline conditions, copper(II) ions form a complex with the -CO-NH- peptide bonds, producing a violet color whose intensity is proportional to the number of peptide bonds in the sample. Since the number of peptide bonds roughly increases with the amount of protein, the assay provides a measure of total protein regardless of protein type. Other components like hemoglobin, carbohydrate chains, or lipids don’t form the same copper-peptide complex and thus don’t drive the signal. Dipeptides have one peptide bond, polypeptides have more, so more protein yields more bonds and a stronger color.

Biuret method relies on the presence of peptide bonds in proteins. In alkaline conditions, copper(II) ions form a complex with the -CO-NH- peptide bonds, producing a violet color whose intensity is proportional to the number of peptide bonds in the sample. Since the number of peptide bonds roughly increases with the amount of protein, the assay provides a measure of total protein regardless of protein type. Other components like hemoglobin, carbohydrate chains, or lipids don’t form the same copper-peptide complex and thus don’t drive the signal. Dipeptides have one peptide bond, polypeptides have more, so more protein yields more bonds and a stronger color.