From Kinetics of OH Reaction with Glutamic Acid to Oxidative Damage to Proteins.

Hydroxyl (OH) is a radical that is distributed all over the universe including the human body, where it can be readily produced, results in oxidative damage to cellular components, and leads to several health implications. While the reaction of OH with proteins is usually addressed as the gas-phase reaction of free amino acids with OH in theoretical studies, this study questions the efficiency of such calculations by focusing on the reaction of glutamic acid (Glu) with OH. According to the results, the reaction profile alters significantly by shifting from gas-phase calculations to solvent-phase due to the zwitterionic nature of this amino acid. So that the barrier height of the N-terminal reaction path and the relative energies of the species vary considerably. Furthermore, the interconnection of all collisional energy transfer events and chemical changes through solving the reaction's master equation and inclusion of the effect of tunneling suggests that the major product changes from vdw1-N to R-CA, R-CB, and R-CG by considering the effect of solvent on the gas-phase reaction. Despite these changes, the rate constants of both gas- and solvent-phase reactions (1.23 × 1010 and 7.32 × 109 L mol-1 s-1, respectively, at 310 K and 1 atm) demonstrate positive temperature dependency. With respect to the rate coefficients reported in the literature, Glu, Ser, and Met are the most vulnerable amino acids to oxidative attack by OH among the Ser, Cys, Asn, β-Ala, Ala, Gly, Met, and Glu amino acids.