Enzymic Synthesis of Dimethyl Selenide from Sodium Selenite in Mouse Liver Extracts

Abstract

The enzymic synthesis of dimethyl selenide from sodium selenite was studied with mouse liver extracts as a model system for the reductive utilization of selenium. Dimethyl selenide was identified as the major volatile product in doubly labeled studies with carbon-14 and selenium-75. Both the 165,000 X g supernatant fraction of liver and washed microsomes synthesize dimethyl selenide, but neither fraction is as active as a 9000 X g supernatant fraction. Activity is proportional to protein concentration, and heated extracts are inactive. Optimal conditions were determined for the over-all reaction. The crude system has a specific requirement for glutathione that cannot be eliminated by various thiols or by dithiothreitol. 5-Adenosyl-l-methionine is the probable methyl donor. Reduced triphosphopyridine nucleotide, coenzyme A, adenosine 5'-triphosphate, and magnesium are also required for optimal activity. Incubation under nitrogen increases the yield of dimethyl selenide approximately tenfold compared to incubation in air, apparently by preventing the oxidation of labile reduced forms of selenium. The crude system is inhibited 50% by 10-6 m arsenite in the presence of a large excess of thiols and is also inhibited by cadmium. The possible role of glutathione derivatives of selenium in the synthesis of organoselenium compounds is discussed. © 1966, American Chemical Society. All rights reserved.