INVOLVEMENT OF PROTEIN SOLVATION IN THE INTERACTION BETWEEN A CONTRAST-MEDIUM (IOPAMIDOL) AND FIBRINOGEN OR LYSOZYME

The interaction between proteins and a radiological commonly-used cont rast medium (iopamidol) have been studied by calorimetry. When aqueous solutions of fibrinogen or of lysozyme (20 g/l) are mixed with an aqu eous solution of iopamidol (1,3-5 l]-5-[(2-hydroxy-1-oxopropyl)amino]- 2,4,6-triiodo) in the clinical blood concentration range (26-485 mM), isothermal calorimetry reveals a weak endothermal interaction at a hig h concentration of iopamidol for both proteins. This endothermal effec t does not appear to be due to direct protein-iopamidol association. D ifferential scanning calorimetry confirms the influence of iopamidol b y the change in protein unfolding in the presence of contrast medium, and suggests alterations in the protein solvation as a mechanism. Dilu tion studies indicate that iopamidol can influence protein solvation e ven when water molecules are present in a molecular excess of 1000. Th e influence of iopamidol on the availability of water molecules and th e absence of direct interaction with the protein molecules is shown by Raman spectroscopy of two amino acids in the presence of iopamidol. T he spectrum of alanine is unchanged at any iopamidol concentration stu died, whereas the spectrum lines due to the thiol group of cysteine ar e shifted in a manner consistent with altered solvation.