V. Letilly et al., PULSE-RADIOLYSIS REDUCTION OF MYOGLOBIN - HYDRATED ELECTRONS DIFFUSION INSIDE THE PROTEIN MATRIX, Journal of the American Chemical Society, 119(44), 1997, pp. 10810-10814
Pulse radiolysis studies have demonstrated that the kinetics of myoglo
bin reduction changes with the pH of the solution. The reduction rate
constant of the protein decreases with increasing pH. The net charge o
f the macromolecule was longtime considered to be responsible for this
dependence. However, for every protein molecule bearing many reductio
n sites, the reduction rate of the protein would be the summation of t
he individual reactions of hydrated electrons on each particular reduc
ible site. The two schemes of protein reduction were checked by the in
vestigation of the behavior of the experimental reduction constant val
ues (i) versus the protein charge (Bronsted approach) and (ii) versus
the reducible imidazolium groups number of the protein. Although the t
wo plots are linear and seem to assert that the two approaches are equ
ivalent, a critical analysis sho ws that the Bronsted formulation cann
ot be applied to proteins. This scheme gives also erroneous different
radii for the same protein. Thus, this work rationalizes the pH-depend
ent rate of reduction by an interaction of the hydrated electron with
protonated histidine residues of the protein.