Qualitative tests of functional groups in Protein

 Qualitative tests of functional groups in Protein 

Aim:-   Detection of  Protein 

Preparation of Sample solution for protein test. 

For experiments fresh 5% solution of egg white is prepared. Egg white is filtered through cotton. Dissolve 5ml  of egg white into 95 ml of distilled water for 5% egg white solution. Proteins show both precipitation and colour reactions. 

Preliminary test for identification of unknown substance from the sample

Sr. No.	Test	Observation	Inference
1	Preliminary Test	coagulation	Protein  may be present carbohydrates may be present
		No coagulation	carbohydrates may be present
2	Biurate test Take 3 ml  of 5% O.S. in a test tube, add 1 ml of 40% NaOH solution to make it strongly alkaline, and then add 2 drops of 1 % copper sulphate solution.	Violet or pink colour appears.	Protein may be present.
3		No violet or pink colour	Carbohydrates may be present.

 

 Qualitative tests of functional groups in Protein 

Test for Protein

Proteins, found in animals and plants are important building blocks formed by amino acids, condensed together by a peptide linkage. They contain free amino and carboxyl groups and so they can combine with bases and acids depending upon the pH of the medium. On hydrolysis, proteins break into peptones, proteoses, peptides and amino acids. Chemical behaviour of the proteins is due to the amino acids in the protein molecules.

           

Sr. No.	Test	Observation	Inference
1	Mercuric chloride test. In a test tube take 3 ml  of 5% O.S. then add mercuric chloride drop by drop.	White turbidity is produced first which becomes thick and granular.	Protein is present
2	Precipitation of proteins with heavy metals  O.S+Hgcl2 drop by drop + lead acetate	White ppt.	Protein present
3	Hellers' test. (Ring test) Take 3 ml of concentrated HN03 in a test tube and then add very carefully 3 ml of 5% egg white solution by means of a pipette in such a manner that it forms upper layer.  Mix gradually by rotating between palms.	A white ring is formed at the junction of the two solutions.	Protein is present
4	Ninhydrin test. Take 1 ml  of 5% O.S.  and add 4 drops of 0.1 % ninhydrin solution and boil for one minute. Cool the test tube.	Blue colour develops.	Protein present
5	Xantho protein Recn  O.S. + 1ml HNO3(conc.) & then boil	White ppt turns Yellow after boiling	Protein confirmed
6	Million test:- O.S.. +2ml HgSo4 boil cocl+ few drops of NaNO2 then heat	Yellow to dark red ppt	Protein confirmed

 

Result: The given sample contains protein.