Role of electrostatic forces in hydroxy and keto bile salt-albumin interactions: some experimental observations.

Proton binding to bovine serum albumin and effects on hydroxy and keto bile salts-albumin binding were studied within a pH range between 5 and 10. Electrostatic forces contribute to the binding of these ligands to albumin; prototropic groups of albumin such as imidazol are involved in the interaction. Bile salts binding produces a shift in pK of these groups. It is postulated that hydroxy bile salt-albumin binding is linked with the N in equilibrium with B transition of the protein, while for keto bile salts a microarrangement in the protein binding sites is driving the interaction.     

How Flexible Polymers Interact with Proteins and Its Relationship with the Protein Separation Method by Protein–Polymer Complex Formation

Bovine serum albumin was selected as a model protein to study the molecular mechanism of interaction between flexible polymer with net negative electrical charge (polyvinylsulphonate and polyacrylic acid) and a non-charged polymer such as poly(ethylene) poly(propylene) oxide (molecular mass 8,400) by using spectroscopies techniques combination: fluorescence emission and circular dichroism. Polyvinylsulphonate and polyacrylic acid interact with the protein due to the coulombic interaction between positive charged protein groups such as amine of lysine and histydine. The poly(ethylene)-poly(propylene) oxide increased the hydrophobic microenvironment around the tryptophan residues. This polymer preserved the secondary and tertiary structure of the protein and did not induce any significant modification in the protein surface area exposed to the solvent.     

Chymotrypsin — Eudragit® complex formation

Eudragit® L100 (EuL) and Eudragit® S100 (EuS) are synthetic polyanions differing on their electric charge density. They interact with chymotrypsin (ChTRP), a basic protein forming soluble and non-soluble complexes. The complex formation was studied by dynamic light scattering, isothermal titration calorimetry, native fluorescence emission, circular dichroism and thermodynamical thermal stability of the enzyme. EuS was able to bind 33 ChTRP molecules while EuL, 60. The binding of ChTRP to both Eu was slightly endothermic and the entropic factor was responsible for the soluble complexes formation. The ChTRP-Eu size increases with pH and the binding of ChTRP to Eu modifies the Eu hydrodynamic radium. The interaction of ChTRP with Eu did not modify its secondary or tertiary structure. The thermal stability of ChTRP was increased when it interacted with both Eu.