One-electron reduction of selenomethionine oxide

Experimental evidence is provided that selenomethionine oxide (MetSeO) is more readily reducible than its sulfur analogue, methionine sulfoxide (MetSO). Pulse radiolysis experiments reveal an efficient reaction of MetSeO with one-electron reductants, such as e(aq)(-) (k = 1.2 x 10(10) M-1 s(-1)), CO2.- (k = 5.9 x 10(8) M-1 s(-1)) and (CH3)(2) (COH)-O-. (k= 3.5 x 10(7) M-1 s(-1)), forming an inter mediate selenium-nitrogen coupled zwitterionic radical with the positive charge at an intramolecularly formed Se therefore N 2 sigma/1 sigma* three-electron bond, which is characterized by an optical absorption with lambda(max) at 375 nm, and a half-life of about 70 ps. The same transient is generated upon HO. radical-induced one-electron oxidation of selenomethionine (MetSe). This radical thus constitutes the redox intermediate between the two oxidation states, MetSeO and MetSe. Time-resolved optical data further indicate sulfur-selenium interactions between the Se therefore N transient and GSH. The Se therefore N transient appears to play a key role in the reduction of selenomethionine oxide by glutathione.