Size-dependent tuning of horseradish peroxidase bioreactivity by gold nanoparticlesElectronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07056a

• Main Authors: Wu, Haohao, Liu, Yi, Li, Meng, Chong, Yu, Zeng, Mingyong, Lo, Y. Martin, Yin, Jun-Jie
• Format: Journal Article
• Language: English
• Published: 26.02.2015
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c4nr07056a

Molecules with diverse biological functions, such as heme peroxidases, can be useful tools for identifying potential biological effects of gold nanoparticles (AuNPs) at the molecular level. Here, using UV-Vis, circular dichroism, dynamic light scattering, and electron spin resonance spectroscopy, we report tuning of horseradish peroxidase (HRP) bioactivity by reactant-free AuNPs with diameters of 5, 10, 15, 30 and 60 nm (Au-5 nm, Au-10 nm, Au-15 nm, Au-30 nm and Au-60 nm). HRP conjugation to AuNPs was observed with only Au-5 nm and Au-10 nm prominently increasing the α-helicity of the enzyme to extents inversely related to their size. Au-5 nm inhibited both HRP peroxidase activity toward 3,3′,5,5′-tetramethylbenzidine and HRP compound I/II reactivity toward 5,5-dimethyl-1-pyrroline N -oxide. Au-5 nm enhanced the HRP peroxidase activity toward ascorbic acid and the HRP compound I/II reactivity toward redox-active residues in the HRP protein moiety. Further, Au-5 nm also decreased the catalase- and oxidase-like activities of HRP. Au-10 nm showed similar, but weaker effects, while Au-15 nm, Au-30 nm and Au-60 nm had no effect. Results suggest that AuNPs can size-dependently enhance or inhibit HRP bioreactivity toward substrates with different redox potentials via a mechanism involving extension of the HRP substrate access channel and decline in the redox potentials of HRP catalytic intermediates. Here we report gold nanoparticles can size-dependently enhance or inhibit HRP bioreactivity toward substrates with different redox potentials via a mechanism involving extension of the HRP substrate access channel and decline in the redox potentials of HRP catalytic intermediates.