CONFORMATIONAL-CHANGES AND PHYSICOCHEMICAL PROPERTIES OF TRANSFERRIN UPON DERIVATIZATION WITH CHOLESTEROL

Transferrin was chemically modified by covalent linkage of cholesteryl oxycarbonyl-6-aminohexanoic acid to the lysine amino groups. Cholester yloxpcarbonyl-6-aminohexanoic acid was prepared from cholesteryl chlor ocarbonate and 6-aminohexanoic acid. This derivative was attached by a n amide bond to the free amino groups of transferrin. The level of der ivatization was quantitated by amino acid analysis and determination o f free amino groups by the trinitrobenzene sulfonic acid method. The p hysicochemical characteristics of native and derivatized transferrin w ere studied by several methods. Surface activity was determined by the pressure increases at the air/water interface. Surface hydrophobicity was checked by anilino naphthalene sulfonic acid titration. Lipid-pro tein interactions were determined by intrinsic fluorescence changes, w ith the bilayers in the fluid and gel state. The results obtained show that derivatization renders the protein highly hydrophobic. Neverthel ess, the surface activity or the interaction with lipids do not correl ate with the hydrophobicity of the molecule, thus suggesting the forma tion of some type of internal micelles or a strongly packed structure.