Identification of inherently antioxidant regions in proteins with radical-directed dissociation mass spectrometry.

Antioxidant peptides such as glutathione play critically important roles within cells by opposing the action of oxidative species. Similarly all proteins may, as a secondary function, potentially contribute to the antioxidant capacity of the cellular milieu, though this possibility has not been thoroughly explored previously. Herein it is demonstrated that, in addition to radical quenching solution-phase behavior, antioxidant peptides display an astonishing ability to sequester radicals in the gas phase. Compared to other peptides of similar sequence and size, radical antioxidant peptides exhibit very little radical-directed dissociation when subjected to collisional activation in the gas phase. Importantly, this property can be leveraged in highly sensitive and rapid mass spectrometry based experiments to identify antioxidant peptides. Examination of peptides derived from human serum albumin (HSA), which is a protein known to behave as an antioxidant, revealed three previously unknown peptide regions that exhibit antioxidant capacity. One of these peptides, VAHRFK, shows antioxidant capacity comparable to that of glutathione. It is likely that these peptide regions contribute to the overall antioxidant capacity of HSA. In comparison with previous methods, the present technique is significantly more sensitive and less time-consuming, which should enable more wide-scale examination of antioxidant peptides that are relevant to redox homeostasis, food chemistry, and disease.