**6.1 Transformation, absorption and transport**

Glutathione plays a major role in the metabolism of selenium; it is involved in reduction reactions where selenite is converted to hydrogen selenite (H2Se) which further releases the selenium for selenoprotein synthesis. The hydrogen selenide undergoes several methylations to finally arrive at formation of trimethylselenonium ion [(CH3)3Se+ ] [57]. The rate of absorption of selenite in sheep much lower (29%) when compared with pork (80%) while selenate and selenomethionine have greater absorption rate in poultry animals. This is a result of reduction of selenite that is not available in ruminants [40]. Absorption occurs mostly inside the caecum and duodenum by active transport via a sodium pump. The mode of action differs depending on the specific form of selenium. Adsorption could be by simple diffusion e.g. selenite or by cotransport while the selenomethionine are absorbed via the amino acid uptake method [52, 58]. Elements like lead, sulfur and arsenic slows down the rate of absorption of selenium either through competing with selenium or by formation of complexes that are not capable of being assimilated [59]. Selenium level in the hepatocytes determines the level of absorption in the intestine. Erythrocytes take up selenium rapidly and it undergoes reduction by glutathione reductase and finally

**Figure 2.** *Selenium metabolism in plants.*

transported in the form of selenide in the plasma to the liver [60]. Selenium can also bind to either α and β globulins and can be transported in the form of selenoprotein by the blood [40].
