Stabilność hemoglobiny Chironomus thummi thummi w układzie rozpuszczalników woda-glikol etylenowy. Badanie mechanizmu denaturacji Hb CTT

Qualitative analysis of the effect of ethylene glycol (EG) on the stability of the native structure of monomeric and dimeric methemoglobins isolated from larvae of Chironomus thummi thummi (CTT Hb) was performed by measurements of thermodynamic parameters of denaturation employing the equilibrium method. Results of denaturation studies at various pH conditions demonstrate that the stability of dimeric CTT Hb is close to that of human Hb while monomeric components show a highter lability. The dependence of denaturation enthalpy on the EG concentration is slightly different for monomeric and dimeric components. For dimeric Hb a considerable decrease of denaturation energy was found already at very low EG concentration which is probably due to the disturbance of interaction between the dimeric - forming chains and, as a consequence, to their dissociation. The futher course of the curves is similar for both Hb deriveratives: an increase in the denaturation energy is observed, peaking at the EG molar fraction of 0.04-0.05, folowed by its rapid decrease. The obtained results are in agreement with the following hypothesis. The structal and dynamic stability of globular proteins is controlled by interactions with the surrounding water molecules. Addition of an organic solvent, possessing both hydrophilic and hydrophobic properties as EG, to the medium, disturbs the native protein conformation by change of the structure of its hydration shell. At appropriate concentrations, EG makes the protein to acquire the supernative structure which is reflected by changes in absorption spectra in the UV range demonstrating alterations in the surrounding of the hydrophobic residues. Highter EG concentrations are sufficient to form a new hydration shell of the protein molecule enducing its different special organization.