COLOR REACTION OF PROTEINS

• a chemical reaction that is used to transform colorless chemical compounds into colored derivatives which can be detected visually.

  color reaction
• blue → pink / pale violet


  Biuret Test for Peptide Bonds
• yellow → deep blue / violet color


  Ninhydrin Test for Free Alpha-Amino Group
• yellow → orange


  Xanthoproteic Test for Phenyl-Containing Amino Acids
• violet ring


  Adamkiewicz Reaction for Tryptophan
• black ppt


  Reduced Sulfur Test for Cysteine
• violet ring


  Molisch’s Test for Presence of Carbohydrate Moiety
• canary yellow precipitate


  Modified Neuman’s Test for Phosphate Moiety
• Biuret test, also known as?

  Piotrowski’s test
• general test for the presence of proteins which is dependent on the presence of peptide bonds.

  Biuret Test
• The intensity of the violet color is (?) proportional to the amount of peptide bonds present

  directly
• A minimum of (?) peptide bonds is required to give a positive result.

  2
• a general test for the presence of proteins which is dependent on the presence of free alpha-amino groups.

  Ninhydrin Test
• The liberated NH3 goes on to react with another ninhydrin molecule to form?

  diketohydrin
• diketohydrin is a colored complex, which is also known as?

  Ruhemann’s purple
• it will give a yellow color with ninhydrin.

  Proline
• it will give a brown color

  Amino acids with amide group, asparagine, and glutamine
• used to indicate the presence of amino acids containing phenyl (benzene) ring in proteins


  Xanthoproteic Test
• is a specific test for the presence of the amino acid tryptophan.


  Adamkiewicz reaction
• is a specific test for the presence of the amino acid cysteine.

  Reduced Sulfur Test
• When cysteine or cysteine-containing proteins are boiled with strong alkali, organic sulfur splits and forms sodium sulfide, which on addition of lead acetate produces?

  lead sulfide (black ppt)
• it does not answer the reduced sulfur test

  Methionine
• contain only amino acid components.

  Simple proteins
• contain amino acids and non-amino acid groups called prosthetic groups.


  conjugated proteins
• is a general qualitative test for the presence of carbohydrates in solution

  Molisch’s test
• A protein with carbohydrate prosthetic group is known as ?

  glycoproteins
• A conjugated protein containing a phosphate group is known as a?

  phosphoprotein