Molecular insights into the interaction between cytochrome and carbon nanomaterials.

Carbon nanomaterials (CNMs) are a heterogeneous class of advanced materials. Their widespread use is associated with human safety concerns, which can be addressed by safe-by design strategies. This implies a deep knowledge of how physico-chemical properties drive biological effects. The ability of CNMs to interact with cytochrome (cyt ), a heme-protein playing a key role in the respiratory chain, in apoptosis and in cellular redox homeostasis, has been reported in some studies. However, the consequences of this interaction on the cyt functions are controversial. Here the mechanism of interaction of carbon nanoparticles (CNPs), chosen as model of redox-active CNMs, with cyt has been studied with the aim to shed light into these discrepancies. The effect of CNPs on the redox state of cyt was monitored by UV-vis spectroscopy and 1D H NMR, while the effect on the primary, secondary, and tertiary cyt structure was investigated by FIA/LC-MS and Circular Dichroism (CD). Finally, the peroxidase activity of cyt and the involvement of superoxide radicals was evaluated by EPR spectroscopy. We demonstrate the existence of two mechanisms, one leading to the suppression of the cyt peroxidase activity following the NADH-independent reduction of the heme-iron, and the other resulting in the irreversible protein unfolding. Overall, the results suggest that these two processes might be independently modulated by redox and surface properties respectively.