Interactions of Two Amphiphilic Penicillins with Myoglobin in Aqueous Buffered Solutions:  A Thermodynamic and Spectroscopy Study

Abstract

The interactions and complexation process of the amphiphilic penicillins sodium cloxacillin and sodium dicloxacillin with horse myoglobin in aqueous buffered solutions of pH 4.5 and 7.4 have been examined by equilibrium dialysis, zeta-potential, isothermal titration calorimetry (ITC) and UV-Vis absorbance techniques. A more opened structure of the protein molecules is detected as a consequence of the reduction of pH from 7.4 to 4.5. Binding isotherms and derived Hill coefficients reflect a cooperative binding behavior. Gibbs energies of binding per mole of drug were obtained from equilibrium dialysis data and compared with those derived from the zeta potential taking into account cooperativity. DeltaGads degrees values so obtained are large and negative at low concentrations where binding to the "high-energy" sites occurs and decreases with the drug concentration. The enthalpies of binding have been obtained from ITC and are small and exothermic so that the Gibbs energies of binding are dominated by large increases in entropy consistent with hydrophobic interactions. Other thermodynamic quantities of the binding mechanism, that is, entropy, DeltaSITCi, Gibbs energy, DeltaGITCi, the binding constant, KITCi, and the number of binding sites, ni, were also obtained, confirming the above results. From ITC data and following a theoretical model, the number of bound and free penicillin molecules was calculated, being higher at pH 4.5 than at pH 7.4. The binding of penicillin causes a conformational transition on protein structure as a consequence of the resulting intramolecular repulsion between the penicillin molecules bound to the protein. Thermodynamic quantites (the Gibbs energy of the transition in water, DeltaGw degrees , and in a hydrophobic environment, DeltaGhc degrees) of the denaturation process were calculated, indicating that at pH 4.5 some of the histidine residues are protonated, becoming accessible to solvent and giving rise to a more opened protein structure.

Microencapsulated Solid Lipid Nanoparticles as a Hybrid Platform for Pulmonary Antibiotic Delivery

“…In the case of mannitol (Figure A,C), the enthalpy of interaction ( Δ H i i , the superscript denoting the binding site) with SLN is rather more negative than that of trehalose (Figure B,D), and hence, the complexation process is exothermic and becomes progressively less negative as the SLN/mannitol molar ratio increases, as observed for other systems such as protein–drug and polyelectrolyte–polyelectrolyte systems . The negative Δ H i i values can be originated from extensive hydrogen bonding network formation between fatty acids comprising both types of SLN and hydroxyl groups of mannitol.…”

“…In the case of mannitol (Figure 4A,C), the enthalpy of interaction (ΔH i i , the superscript denoting the binding site) with SLN is rather more negative than that of trehalose (Figure 4B,D), and hence, the complexation process is exothermic and becomes progressively less negative as the SLN/mannitol molar ratio increases, as observed for other systems such as protein− drug and polyelectrolyte−polyelectrolyte systems. 31 The negative ΔH i i values can be originated from extensive hydrogen bonding network formation between fatty acids comprising both types of SLN and hydroxyl groups of mannitol. Increase in SLN concentration leads to a progressive increase of ΔH i i (less exothermic) due to surface dehydration of SLN and excipient molecules upon mutual interaction, although contributions from a certain SLN charge shielding and excipient's molecular rearrangements upon excipient adsorption onto SLN surfaces could not be neglected.…”

Ferrocene‐Substituted Dithio‐o‐Carborane Isomers: Influence on the Native Conformation of Myoglobin Protein

“…Clearly, the heme environment of Mb is profoundly affected by the ferrocene–carborane conjugates as observed by the remarkable change of the Soret CD band. In Mb, the heme prosthetic group is totally buried in a hydrophobic cleft formed by helixes A to H. Hydrophobic interactions between the tetrapyrrole ring and the hydrophobic amino acid groups on the interior of the cleft could strongly stabilize the heme protein conjugates 11a. FcSB1 and FcSB2 could easily gain access to the heme pocket owing to their hydrophobic properties.…”

Multifaceted Analysis of the Noncovalent Interactions of Myoglobin with Finely Tuned Gemini Surfactants: A Comparative Study

“…Generally, hydrophobic molecules are able to traverse the membrane by dissolving in the lipid bilayer. , Thus, C m –E2O–C m gemini surfactants (because of their higher hydrophobic character) can penetrate the plasma membrane, leading to interaction with heme proteins such as Mb. Furthermore, several drugs, mainly those with local anesthetic, tranquilizer, antidepressant, and antibiotic actions, exert their activity by interaction with biological membranes and, thus, can penetrate the membranes of the muscle cells, thereby becoming exposed to Mb . Therefore, investigations on the interaction of green gemini surfactants, which are generally employed as excipients in drug formulations and other associated applications, with Mb are of great importance, in terms of understanding their roles in biological processes.…”