The protein and biuret color-change reaction is a reaction in which the charge of copper ions in the biuret reagent change from a +2 to a +1 in the presence of the peptide bonds that hold amino acids together. This alteration causes a color change from blue to purple.
Biuret reagent is an alkaline mixture consisting of potassium hydroxide and copper sulfate. It is often used to test for protein in human urine or in the human bloodstream. A significant reaction of biuret reagent with protein in human urine analysis can indicate problems with the function of the kidneys, diabetes, heart disease or other health problems. It may also be an indication of pregnancy. A significant reaction of biuret reagent with protein in the bloodstream is often used to diagnose dehydration, inflammation or infection.
Proteins are made up of amino acids connected to each other by peptide bonds. Though there are 50 amino acids in the human body, only 20 amino acids are used to make proteins. The amino acids are connected by peptide bonds in various combinations to create the many different proteins that are essential for cellular processes. At least two peptide bonds must exist for biuret reagent to indicate the presence of a protein.