Physical properties of proteins

Physical and chemical properties of protein
    • Pure proteins are generally tasteless, though the predominant taste of protein hydrolysates is bitter.
    • Pure proteins are odourless. Because of the large size of the molecules, proteins exhibit many properties that are colloidal in nature.
    • Proteins, like amino acids, are amphoteric and contain both acidic and basic groups.
    • They possess electrically charged groups and hence migrate in an electric field.
    • Many proteins are labile and readily modified by alterations in pH, UV radiation, heat and by many organic solvents.
    • The absorption spectrum of protein is maximum at 280 nm due to the presence of tyrosine and tryptophan, which are the strongest chromophores in that region.
    • Hence the absorbance of the protein at this wavelength is adapted for its determination

    Denaturation of protein
    • The comparatively weak forces responsible for maintaining secondary, tertiary and quaternary structure of proteins are readily disrupted with resulting loss of biological activity
    • This disruption of native structure is termed denaturation
    • Physically, denaturation is viewed as randomizing the conformation of a polypeptide chain without affecting its primary structure.
    • Physical and chemical factors are involved in the denaturation of protein.
    • Heat and UV radiation supply kinetic energy to protein molecules causing the atoms to vibrate rapidly, thus disrupting the relatively weak hydrogen bonds and salt linkages.
    • This results in denaturation of protein leading to coagulation.Enzymes easily digest denatured or coagulated proteins.
    • Organic solvents such as ethyl alcohol and acetone are capable of forming intermolecular hydrogen bonds with protein disrupting the intramolecular hydrogen bonding.
    • This causes precipitation of protein.Acidic and basic reagents cause changes in pH, which alter the charges present on the side chain of protein disrupting the salt linkages.
    • Salts of heavy metal ions (Hg2+, Pb2+) form very strong bonds with carboxylate anions of aspartate and glutamate thus disturbing the salt linkages.
    • This property makes some of the heavy metal salts suitable for use as antiseptics.

    Renaturation
    • Renaturation refers to the attainment of an original, regular three-dimensional functional protein after its denaturation.
    • When active pancreatic ribonuclease A is treated with 8M urea or ßmercaptoethanol, it is converted to an inactive, denatured molecule.
    • When urea or mercaptoethanol is removed, it attains its native (active) conformation.

Last modified: Tuesday, 27 March 2012, 11:38 PM