 Denaturation; It is a process that leads to the protein losing its native 3 dimensional confirmation to a random confirmation without affecting its primary structure.  Factors that cause denaturation of proteins include; - Extreme pH values (strong acids and strong bases ), detergents (urea ), heavy metals (Ag, Pb, Hg), high temperatures, high concentrations of alcohol, or radiation.  Consequences of denaturation include ; - Breaking of weak bonds such as ; Hydrogen bonds,Ionic bonds, hydrophobic interactions, Vander Wall forces, (the peptide bond is not affected by denaturation). -The protein becomes less soluble thus tends to coagulate (precipitate out of the solution). - It loses its native unique conformation and adopts a random confirmation. -It loses its biological function.

-The proteins lose their secondary, tertiary and quaternary structure. Following denaturation, some proteins will return to their native structures under proper conditions; but extreme conditions, such as strong heating, usually cause irreversible denaturation.

 1-Proteins show a peak absorbance at 280nm due to the presence of aromatic amino acids.  2-Proteins are charged molecules. The net charge on the protein is determined by the α-amino,α-carboxyl, and the ionizable groups of the side chains, which are affected by the pH of the solution.Proteins at pH values higher than their pI carry a net negative charge, at pH values lower than their pI they carry a net positive charge, and at pH values equal to their pI their net charge is zero. Protein(+) migrates to anode, Protein(0) does not move, At pH<pI, At pH=pI, Protein (-) migrates to cathode At pH > pI

CHMI E.R. Gauthier, Ph.D. 5 ProteinpI Pepsin1 Egg albumin4.6 Serum albumin4.9 Urease5  -lactoglobulin 5.2 Hemoglobin6.8 Myoglobin7 Chymotrypsinogen9.5 Cytochrome c10.7 Lysozyme Proteins have distinctive isoelectric points pI. At the isoelectric point proteins are least soluble, since the net charge on the protein molecules is zero thus no repulsion forces exist between the protein Molecules allowing interactions to occur between opposite charges on protein molecules,thus increasing protein-protein interactions and decresing protein –water Interactions explaining the low solubility.

4 -Proteins can be precipitated by heavy metals such as Ag, Pb,Hg Heavy metal ions precipitate proteins from their solutions by cross-linking free amino groups and carboxylate groups. ons commonly used for testing for the presence of proteins include Zn 2+, Fe 3+, Cu 2+, Sb 3+, Ag 1+, Cd 2+, and Pb 2+.Among the metal ions, Hg 2+, Cd 2+, and Pb 2+ have very high toxicity.. They cause serious damage to proteins (especially enzymes) by denaturing them. Victims who have swallowed Hg2+ or Pb2+ ions are often treated with an antidote of a food rich in protein. The protein can combine with the mercury and lead ions and minimize absorption of these ions. Milk and raw egg white are used most often. The precipitated protein complexes are then immediately removed from the stomach by an emetic.

5-Proteins can be detected by the Biuret test. The biuret test is a chemical test used to detect the presence of peptide bonds.In the presence of peptides, cupric ions form a violet colored compound in an alkaline solution. The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, thus it can be used for qualitative and quantitative protein analysis.

 6- Solubility of proteins; The solubility of proteins in aqueous depends on the distribution of hydrophilic and hydrophobic amino acid residues. Proteins that have a large number of hydrophobic amino acid residues on the surface have low solubility in aqueous solvents, whereas proteins that have a large number of hydrophilic amino acid residues on the surface have a higher solubility in aqueous solvents.  7- Precipitation of proteins ; Proteins can be precipitated selectively by high salt concentrations.