Test for proteins and amino acids Flashcards
What are the common tests for proteins
- Biuret test
- Hopkins-cole test
- Millon’s Test
- Xanthoproteic test
- Reduced sulfur test
- Nitroprusside test
- Sakaguchi test
The compounds having two or more peptide bonds and copper salts in alkaline solution create a purple color complex
Biuret test
This test is a confirmatory test the presence of amino acid tryptophan (indole group).
Hopkins-cole test
what is the result of a Hopkin-cole reagents result?
the formation of purple or violet color ring at the interface.
This test is used to detect the presence of phenolic group-containing amino acids like tyrosine.
Millon’s test
This test is identification test for the presence of aromatic amino acids.
Xanthoproteic test
what is the result of Xanthoproteic test>
Orange color
This is a test for sulfur containing amino acids cysteine and cystine (except for methionine where its sulfur is not reactive).
Reduced sulfur test
What does reduced suflur test result to?
black lead sulfide
is a biochemical test used for the detection of the free –SH groups in amino acids or the cysteine amino acid in a protein.
Nitroprusside test
What color does nitroprusside test results to?
Red-colored compound
This test is given by guanidine compounds for example arginine
Sakaguchi test
What color does sakaguchi test result to?
Red color
Procedure of Biuret test
- Mix 2 ml of test solution and 2 ml 10% NaOH
- Add 1 drop of 0.1% CuSO4 solution
- Mix thoroughly and note if a pink or violet color develop
Hopkins-cole test procedure
- take 1 ml of the reagent
- add concentrated H2SO4 along the side of the test tube
Millons test procedure
- Take 2 mL of test sample, add 4 drops of Millon’s reagent.
- Mix well and observe if a white precipitate forms
- Then boil it for 2-5 minutes in a water bath to develop a red color precipitate
Xanthoproteic test
- Add 1ml of test sample and add same amount of conc. HNO3
- Mix well
- Allow it to cool for some time
- Add 1-2 mL of 40% NaOH.
-Orange color is observed if the test is positive
Reduced sulfur test procedure
- Add equala mount of 2ml test sample and 10% NaOH and heat carefully for 15-30- seconds
- Add 5 drops of lead (II) acetate
- If black precipitate of lead sulfide does not form, boil it again.
Nitroprusside test procedure
- Take 2 ml of test sample
- then add 0.5 freshly prepared nitroprusside by shaking the test tube thoroughly
- add sodium hydroxide dropwise
- Watch for red color to indicate positive
Chemicals in Biuret test
10% (w/v) NaOH
0.1% CuSO4 solution
Chemicals in Hopkins-cole test
-Hopkins-cole reagent
-Conc. Sulfuric acid (H2SO4)
Chemicals in Millon’s test
Millon’s reagent
Chemicals in Xanthoproteic test
Concentrated Nitric Acid (HNO3)
10% (w/v) NaOH
Chemicals in Reduced sulfur test
• 10% (w/v) NaOH (same as in Biuret Test)
• 1% Lead acetate
Chemicals in nitroprusside test
• 2% sodium nitroprusside
• 10% (w/v) NaOH (same as in Biuret Test)
Chemicals in sakaguchi test
• 40% (w/v) NaOH
• α-naphthol solution (1% w/v in ethanol)
• 10% sodium hypochlorite
