Thermal reversibility and disaggregation of human serum albumin upon incubation with 3-β hydroxybutyrate: A proposed mechanism for thiol reaction

Thermal inactivation of proteins is a main challenge in food technology and medicine. The 3-β-hydroxybutyrate (3BHB) is the most abundant ketone body with a carboxyl group. Its concentration increases during fasting, prolonged exercise, and in diabetic patients. In this work, human serum albumin (HSA) was incubated with 3BHB for 7, 14, 21, and 35 days under physiological conditions. The thermal reversibility and thermal aggregation of HSA upon incubation with 3BHB were determined by differential scanning calorimetry and free amine content assay. These results indicated that 3BHB binds the lysine residues of HSA through nucleophilic attack leading to formation of covalent bonds. The calorimetric results showed that the modification of lysine residues by 3BHB resulted in partial unfolding of HSA compared to the modification of thiol group of Cys34, which is surrounded by other amino acid side chains. Since thermal aggregation of HSA is related to Cys34, its modification caused a decrease in thermal aggregation and an increase in thermal reversibility of modified HSA.