CHEMISTRY OF PROTEINS

 

CHEMISTRY OF PROTEINS

 

                Proteins are classified into various groups depending upon their solubility. Chemical composition. molecular complexity etc. They are classified as

i.         Simple proteins: Albumin and Globulin of egg.

ii.        Conjugated protein: Casein of Milk.

iii.      Derived proteins: Gelatin, Proteoses and Peptone.

 

                We will take one member from each group and study their reactions like the presence or absence of some particular aminoacids and precipitation reactions.

 

REACTIONS OF ALBUMIN

 

                Albumin is a simple protein which is present in serum, milk, egg and muscles. Albumin has molecular weight of about 69,000. Albumin is the fast moving protein in electrophoresis. It is a glycoprotein. Human serum albumin makes upto about 60% serum protein and contribute 80% of colloidal osmotic pressure.

 

                Albumin is soluble in water, heat coagulable and is precipitated only by full saturation with ammonium sulphate. It is not precipitated by half saturation with ammonium sulphate.

 

(1) Heat Coagulation Test:

                Take 3/4 of the given albumin in test tube, boil the top portion of the solution. The lower portion of the solution which is not heated serves as a control for comparison. A cloudy

white precipitate will be observed in the heated portion.

 

(2) Half Saturation Test:

                To 3ml of albumin solution add an equal volume of saturated ammonium sulphate solution write your inference.

 

(3) Full Saturation Test:

                To 3ml of albumin add solid ammonium sulphate until the solution is saturated. A precipitate is formed.

 

(4) Heller’s Test:

                To 3ml of cone. nitric acid in a test tube add drop by drop albumin solution along the side of tube. A white ring of precipitate is formed.

 

(5) Perform all the colour reactions of proteins and write your conclusions.