| Based on a reported proteinoid microsphere oral drug delivery system, several series of oligopeptides with specific structures and amino acid sequences were synthesized and characterized as potential oral drug delivery carriers for heparin and insulin. Four tetrapeptides were evaluated for sphere formation with protein drugs such as insulin, lysozyme, bovine serum albumin, and heparin. Only pEE(;The interaction of the oligopeptides with heparin was investigated by heparin affinity chromatography, equilibrium dialysis, circular dichroism, differential scanning calorimetry and isothermal titration calorimetry. Only the tetrapeptides with two aromatic amino acids as the terminal residues were retained on a heparin affinity column. The aromatic rings appear to play an important role in the retention of these oligopeptides on the heparin affinity column, in addition to the hydrophobic interactions and H-bonding which were found to be involved in the retention of these oligopeptides. Further heparin affinity chromatography data for the derivatives of the oligopeptide pEE(;The influence of the selected tetrapeptides on insulin was studied by circular dichroism (CD) and isothermal titration calorimetry. The aliphatic pEE(;Currently, the tetrapeptide pEE(... |
