Immobilized metal affinity beads for ferritin adsorption

Abstract

A new metal–chelate adsorbent utilizing N-methacryloyl-(L)-cysteine methyl ester (MAC) was prepared as a metal-chelating ligand. MAC was synthesized by using methacryloyl chloride and L-cysteine methyl ester dihydrochloride. Spherical beads with an average diameter of 150–200 μm were produced by suspension polymerization of 2-hydroxyethyl methacrylate (HEMA) and MAC carried out in an aqueous dispersion medium. Then, Fe³⁺ ions were chelated directly on the beads. Properties such as specific surface area, specific pore volume and ligand occupation were determined. The specific surface area of the beads was found to be 18.9 m²/g. The total pore volume was 2.8 ml/g and represented a porosity over 52%. The average pore size of the poly(HEMA-MAC) beads was 620 nm. Fe³⁺ -chelated beads were used in the adsorption of ferritin from aqueous solutions. Ferritin adsorption increased with increasing ferritin concentration. The maximum ferritin adsorption capacity of the Fe³⁺ -chelated poly(HEMA-MAC) beads (Fe³⁺ loading 0.81 mmol/g) was found to be 3.7 mg/g at pH 4.0 in acetate buffer. The non-specific ferritin adsorption on the poly(HEMA-MAC) beads were 0.4 mg/g. Adsorption behavior of ferritin could be modelled using both the Langmuir and Freundlich isotherms. Adsorption capacity decreased with increasing ionic strength of the binding buffer. Ferritin molecules could be adsorbed and desorbed five times with these adsorbents without noticeable loss in their ferritin adsorption capacity.

Keywords:

• AFFINITY CHROMATOGRAPHY
• METAL-CHELATE AFFINITY BEADS
• CYSTEINE
• FERRITIN
• PHEMA