Synthesis and characterization of hydrophobic ferritin proteins

Alkylated derivatives of the iron storage protein, ferritin, have been prepared by carbodiimide-activated coupling of long chain (C9, C12, C14) primary amines to surface carboxylic acid residues. In the case of a nonyl-derivatized protein, alkylation results in covalent modification of approximately 400 of the 520 amino acid carboxyl groups in the protein molecule. The hydrophobic proteins have a net positive charge in water and can be transferred from THF/water mixtures into dichloromethane, ethyl acetate and toluene by addition of small amounts of NaCl. Transmission electron microscopy, analytical ultracentrifugation, and polyacrylamide gel electrophoresis indicate that the hydrophobic proteins dissolve in the organic solvents as structurally intact, non-aggregated macromolecules which can be subsequently back-extracted into water.