Ferroxidase activity of apoferritin is increased in the presence of platinum nanoparticles

The ferroxidase activity of horse spleen apoferritin (HSAF) is increased by nine-fold in the presence of platinum nanoparticles. HSAF was mixed with varying concentrations of K2PtCl4 followed by a 20-fold concentration of sodium borohydride to afford Pt:HSAF nanoparticle complexes in a ratio of between 1: 250 and 1:4000. Typical colour changes, from colourless or pale yellow to brown, occurred that were dependent on the amount of platinum present. These complexes were characterized by UV/vis, inductively coupled plasma optical emission spectroscopy, Fourier transform infrared, transmission electron microscopy and energy dispersive x-ray spectroscopy. Transmission electron microscopy analysis revealed that the size of nanoparticles increased as the molar ratio of platinum to HSAF increased with an average size diameter of 2-6 nm generated with HSAF: platinum molar ratios of 1:250-1:4000. Fourier transform infrared spectroscopy (FTIR) spectra showed no distinct changes in the structure of HSAF but confirmed that the nanoparticles were attached to the protein. The effect of platinum nanoparticles on the ferroxidase activity of HSAF showed a specific activity of 360 rho mol min(-1) mg(-1), (nine-fold increase over the control) at the molar ratio of HSAF:platinum nanoparticles of 1:1000.