Question

The peptide that gives positive ceric ammonium nitrate and carbylamine tests is:
1. Ser - Lys
2. Gln - Asp
3. Lys - Asp
4. Asp - Gln

Answer 1

Correct Answer - Option 1 : Ser - Lys

Concept:

Ceric ammonium nitrate test is given by alcohol. Only serine(ser) contains –OH group.

Let us consider the Test for Alcohol, it will contain Alcohol, Ceric Ammonium Nitrate which produces the red coloured solution wherein the alcohol is present.

Ceric Ammonium Nitrate (CAN) test involves alcohols that react with the yellow reagent to produce a colour change from yellow to red, but the carbonyl group is unreactive.

Let us consider the carbylamines test, the product is isocyanide and this reaction is used for the detection of primary amines wherein,

RNH₂ + CHCl₃ + 3KOH → R – NC + 3KCl + 3H₂ O

(an isocyanide)

The carbylamines reaction also known as Hoffman's isocyanide test. The Hoffman’s isocyanide test is a chemical test for detection of primary amines. In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed which are foul smelling substances.

An isocyanide (also called isonitrile or carbylamine) is an organic compound with the functional group –N ≡ C. It is the isomer of the related cyanide (-C ≡ N), hence the prefix is isocyano. The organic fragment is connected to the isocyanide group via the nitrogen atom, not via the carbon.

The peptides that gives the positive ceric ammonium nitrate which gives –OH and Positive carbylamines test which gives -NH₂.

Thus, Lysine-Serine peptides gives positive ceric ammonium nitrate and carbylamine tests.