Direct Conversion of L-Selenomethionine into Methylselenol by Human Cystathionine ��-Lyase

Selenium is an essential trace element for mammals, but it is very toxic. Therefore, the control of selenium concentrations should be precisely and effectively monitored. Selenium is naturally obtained through foods and seleno-L-methionine (LSeMet) is a major form of selenium. It has been reported that L-SeMet is only converted into Se-adenosyl-L-SeMet. However, a recent study suggested that L-SeMet was directly metabolized into methylselenol () in mouse liver extract by the reaction of cystathionine -lyase (CGL). The canonical reaction of CGL was known to catalyze the cleavage of L-cystathionine to L-cysteine, -ketobutyrate and . In the present study, we found that L-SeMet could be directly converted to using purified homogenous human CGL instead of mouse liver cytosol. Authentic was prepared by reduction of dimethyldiselenide with sodium tetrahydroborate. The gaseous product of the enzymatic reaction with L-SeMet was analyzed by GC/MS spectrometry. The GC/MS data was identical to that of authentic dinitrophenyl selenoether. We also analyzed the kinetic parameters for the formation of from L-SeMet by human and mouse CGL. These results suggest that human CGL is a critical enzyme which is responsible for L-SeMet metabolism.