Thermodynamics of water binding by human serum albumin suspended in acetonitrile

Abstract

Heat effects resulting from the introduction of solid human serum albumin (HSA) into various water-acetonitrile mixtures were measured calorimetrically at 298 K. The amount of water bound to the suspended HSA as a function of the water content of the solvent was also determined. Introducing HSA into water-acetonitrile mixtures involves water binding according to the Langmuir isotherm with an adsorption constant Kc = 1.0 ± 0.1 M-1, enthalpy Δh = -9.0 ± 1.5 kJ mol-1 and entropy ΔS = -30 ± 6 J mol-1 K-1. Placing HSA in the solvent has an additional heat effect of 46 ± 19 J g-1, which is attributed to an unknown transformation of the protein preparation. © 1995.