Transferrin was chemically modified by covalent linkage of cholesteryloxycarbonyl-6-aminohexanoic acid to the lysine amino groups. Cholesteryloxycarbonyl-6-aminohexanoic acid was prepared from cholesteryl chlorocarbonate and 6-aminohexanoic acid. This derivative was attached by an amide bond to the free amino groups of transferrin. The level of derivatization was quantified by amino acid analysis and determination of free amino groups by the trinitrobenzene sulfonic acid method. The physicochemical characteristics of native and derivatized transferrin were 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-protein interactions were determined by intrinsic fluorescence changes, with the bilayers in the fluid and gel state. The results obtained show that derivatization renders the protein highly hydrophobic. Nevertheless, the surface activity or the interaction with lipids do not correlate with the hydrophobicity of the molecule, thus suggesting the formation of some type of internal micelles or a strongly packed structure. © 1994.

This work was supported by a grant N.BI 092~0982X0 2-02 from CICYT, Spain

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