[Molecular mechanism of oxacillin interaction with human serum albumin studied by microcalorimetry]

Interaction of oxacillin, a semisynthetic penicillin, with human serum albumin (HSA) was studied by means of reaction isothermal and differential scanning microcalorimetry. The antibiotic bound with one primary and two secondary active protein sites. The first bound molecule of the drug had a significant effect on conformation of the biopolymer, which was evident from increased enthalpy and denaturation temperature of the complex as compared to pure HSA. However, the increased thermostability of the serum albumin on its association with oxacillin did not impair the cooperative nature of the thermal denaturation of globular protein. Analysis of the thermodynamic parameters of the complex formation suggested the presence of hydrophobic and electrostatic interactions. The role of electrostatic interaction increased with a decrease in the solution ionic strength.