Behaviour of Human Blood Orosomucoid (Acid Alpha 1-Glycoprotein) in the Presence of Small Aliphatic Alcohols
Abstract
The influence of both methanol and ethanol on the stability of orosomucoid molecule was studied over a broad range of alcohol concentrations (volume fraction 0 - 70%) and pH between 7 and 12. The data obtained by optical methods were compared with information from prediction studies which were focused on the structural features and physicochemical parameters of amino acid in the orosomucoid molecule.
From this analysis the following conclusions can be drawn: (i) ethanol exerts a more pronounced effect on α-helix formation than methanol does, (ii) at higher pH the electrostatic contribution is the crucial effect in the destabilization of the orosomucoid molecule, (iii) out of 12 phenylalanines in the orosomucoid molecule only 1 - 2 are exposed to the solvent; of the residues which are not subjected to substitution appears to be Phe 141, (iv) its neighbor, Tyr 142, appears to be a key residue, the dissociation of which destabilizes one of two longer helical segments of the orosomucoid molecule, (v) the limits of applicability of the four-derivatives of UV spectra with respect to phenylalanines were examined; analysis of the data is recommended on a more precise mathematical basis, taking into consideration the bandwidth of the spectral peaks.