Characterizing the binding interaction between ultrafine carbon black (UFCB) and catalase: electron microscopy and spectroscopic analysis

Widespread exposure to ultrafine carbon black (UFCB) and its ability to cross the lung-blood barrier have raised concerns regarding its safety. Importantly, UFCB can bind with proteins in the biological fluid after entering a biological environment and immediately form a protein corona. The protein corona could govern its further fate in the biological environment. In this work, we investigated the effects of UFCB to the structure and activity of catalase (CAT) to explore its biocompatibility with CAT. FW 200 (13 nm) and tween 80 (T80) were used as the UFCB model and the dispersant. Electron microscopy and dynamic light scattering (DLS) were used to characterize the surface properties and size distribution of UFCB. Steady-state fluorescence combined with synchronous fluorescence and 3D fluorescence show that UFCB bound with CAT and formed the protein corona, resulting an exposure of the internal amino acids (mainly tryptophan and tyrosine) and a decrease of the hydrophobicity of the amino acids. The fluorescence lifetime measurement combined with UV-visible spectra measurement indicated that UFCB quenched the fluorescence of CAT statically and changed the framework of CAT. Circular dichroism (CD) spectra analysis indicated the increase of alpha-helical content and the decrease of beta-sheet structure in catalase, which in turn make the activity of CAT reduce as shown in the enzyme activity assay. The study demonstrated the negative effects of UFCB on proteins and stressed the urgency to conduct more investigation on the biosafety of its application.