Definition of Terms

Biurettest
This is the test indicates the presence of peptide linkages. The purplish to violet color is apparently due to the cupric ions with the unshared electron pairs of four nitrogen atoms. All substance is proportional to the number of peptide bonds give the test and the intensity of the purple color produced id proportional to the number of peptide bonds present.

Ninhydrintest Amino acids react with ninhydrin (tryketoninhydrindene hydrate) to yield CO2, NH3and aldehyde containing one less carbon than the amino acid. The reaction is also yields a blue or purple color useful for the colorimetric determination of amino acids.

X anthoproteictest
This test is positive for proteins and amino acids containing an aromatic side chain (phenylalanine, tyrosine, and tryptophan). The benzene ring undergoes nitration with concentrated HNO3giving nitro derivatives which are yellow in color. Phenylalanine does not response readily to this test and requires H2SO4 as catalyst.

Millon-Nassetest
The phenolic group of tyrosine reacts with Millon-Nasse reagent (HgSO4 in H2SO4) forming an old rose or pink to red complex upon heating. The complex is probably the mercury salt of the phenolic compound

Sakaguchi Reaction
The guanidinium group of arginine in alkaline solution gives an orange or red color with alpha-naphthanol and sodium hypobromite.

Hopkins-Cole test
The indole ring of tryptophan reacts with Hopkins-Cole reagent (glyoxylic acid) and sulfuric acid to produce a violet or red purple color

Objectives
1. To carry out the different color reaction tests for amino acids and proteins;
2. Characterize amino acids based on their reactions with specific chemical reagents;
3. Identify the functional group of the amino acid responsible for the positive color reaction