One-electron reduction of selenomethionine oxide

Experimental evidence is provided that selenomethionine oxide (MetSeO) is m ore 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)), CO 2.- (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 rad ical 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 inter mediate between the two oxidation states, MetSeO and MetSe. Time-resolved o ptical data further indicate sulfur-selenium interactions between the Se th erefore N transient and GSH. The Se therefore N transient appears to play a key role in the reduction of selenomethionine oxide by glutathione.