Amino Acids, Peptides and Proteins

1. Amino Acids, Peptides and Proteins

2. Titration of Amino Acids • Titration of glycine with NaOH

3. Isoelectric Point (pI) • Isoelectric point, pI: the pH at which the majority of amino acid molecules in solution have no net charge • the pI for glycine, for example, falls between the pKa values for the carboxyl and amino groups • the following tables give isoelectric points for the 20 protein-derived amino acids

4. Isoelectric Point (pI)

5. Isoelectric Point (pI)

6. Electrophoresis • Electrophoresis: the process of separating compounds on the basis of their electric charge • electrophoresis of amino acids can be carried out using paper, starch, agar, certain plastics, and cellulose acetate as solid supports • In paper electrophoresis • a paper strip saturated with an aqueous buffer of predetermined pH serves as a bridge between two electrode vessels

7. Electrophoresis • Electrophoresis of a mixture of amino acids

8. Electrophoresis • a sample of amino acids is applied as a spot on the paper strip • an electric potential is applied to the electrode vessels and amino acids migrate toward the electrode with charge opposite their own • molecules with a high charge density move faster than those with low charge density • molecules at their isoelectric point remain at the origin • after separation is complete, the strip is dried and developed to make the separated amino acids visible

9. Electrophoresis • a reagent commonly used to detect amino acid is ninhydrin