Isothermal titration microcalorimetric studies of the effect of temperature on hydrophobic interaction between proteins and hydrophobic adsorbents

This study attempted to comprehend how temperature affects hydrophobic inte raction between proteins and hydrophobic adsorbents. By equilibrium batch a nalysis, we measured the adsorption isotherm to evaluate the protein-adsorb ent affinity, while isothermal titration calorimetry was used to measure th e adsorption enthalpy. In addition, the affinity and enthalpy differences b etween two proteins, alpha-chymotrypsinogen A and trypsinogen, with two ads orbents, butyl-Sepharose and octyl-Sepharose gel, under varying temperature s were studied with respect to the exposed hydrophobic segments of the prot ein and ligand hydrophobicity. The enthalpies obtained in this investigatio n can be used to more thoroughly understand the hydrophobic interaction bet ween proteins and adsorbents. First, the adsorption isotherm experiments re veal that the adsorption quantity of the proteins with the Sepharose gels i ncreases with temperature. For a microcalorimetric measurement, as temperat ure is increased from 298 to 310 K, the Delta H value of alpha-chymotrypsin ogen A with butyl-Sepharose increases, while the Delta H value of trypsinog en is reduced. This is likely due to the fact that alpha-chymotrypsinogen A has a higher area of exposed hydrophobic segments than trypsinogen does. T his observation also implies that as temperature increases, the interaction mechanism of alpha-chymotrypsinogen A with butyl-Sepharose changes from an adsorption-dominated process to a partitioning process. In addition, for o ctyl-Sepharose, the Delta H value of alpha-chymotrypsinogen A is positive a nd decreases with temperature increment. However, the Delta H value of tryp sinogen was positive and increased with temperature. Therefore, we conclude that as temperature increases, the interaction mechanism of the proteins f or octyl-Sepharose is a partitioning-dominated process. (C) 2000 Academic P ress.