Assessment of the Dissociation Energetics of Some Selected Ligand Drugs Bound on Human Serum Albumin by Differential Scanning Calorimetry

Fungicide Tebuconazole Influences the Structure of Human Serum Albumin Molecule

Studies of interactions between pesticides and target mammalian proteins are important steps toward understanding the pesticide's toxicity. Using calorimetric and spectroscopic methods, the interaction between triazole fungicide tebuconazole and human serum albumin has been investigated. The spectroscopic techniques showed that fluorescence quenching of human serum albumin by tebuconazole was the result of the formation of tebuconazole/human serum albumin complex with the static type as the dominant mechanism. The association constant was found to be 8.51 × 103 L/mol. The thermodynamic parameters were obtained as ΔH = -56.964 kJ/mol, ΔS = -115.98 J/mol·K. The main active interactions forming the tebuconazole/human serum albumin complex were identified as the interplay between hydrogen bonds and/or van der Waals forces, based on thermodynamic experiments. These binding modes were corroborated well by the predictions of molecular modeling. Hydrogen bonding of tebuconazole with Arg222, Ala215 and Ala291 of human serum albumin played a relevant role in binding. The conformation changes in secondary structure were characterized by circular dichroism and 3D fluorescence spectra.

Thermally Induced Denaturing Energetics of Human Blood Plasma Albumin by Differential Scanning Calorimetry (DSC) as an Indicator for Breast Cancer Diagnosis in Female Patients

Cancerous invasion yields unusual metabolisms providing a significant amount of peptide albuminomes that modulate albumin stability via binding. The study aimed at the investigation of the thermal stability of human plasma albumin with breast cancer of various stages by means of differential scanning calorimetry (DSC). Blood plasma was drawn from 11 female breast cancer patients and 50 healthy volunteers of homogeneous demographics. Plasma samples and their albumin-enriched fractions were subjected to DSC scanning between 37 and 90°C at 5°C/min rate. For normal blood plasma, a characteristic signature of DSC tracing was observed. And, the deconvolution of DSC thermograms revealed the recognition of thermal transition of albumin. It was found that denaturing temperature of albumin increased with increasing breast cancer staging which implied the increase in albuminome/peptide abundance produced by cancerous invasion. The analysis of albumin denaturing energetics based on rational approximation of the simple Lumry-Eyring model demonstrated that thermal transition of free albumin and albuminome-bound form attained energetic levels expressed as apparent activation energy (E_app ± s.e.) of 132.68 ± 14.21 and 46.76 ± 8.42 Kcal/mol corresponded to the schemes dominated by irreversible alteration and by reversible unfolding, respectively. Thus, E_app value may indicate the degrees of cancerous invasion. It was proposed that E_app may be used as an indicator to diagnose and assess the prognosis of breast cancer.