SELENIUM BIOCHEMISTRY AND DISEASES

Selenium (Se) is a trace element, which is important in many biochemical and physiological process. It is toxic if taken in excess, because it produces an imbalance of nutrients in the diet. Se is incorporated as selenocysteine at the active site of a wide range of selenoproteins, which play an important role in many body functions, including in antioxidant defense and in the formation of thyroid hormones. Some selenoproteins metabolites play a role in cancer prevention. The biochemical role for Se is to regulate enzyme activities as a part of the active site of the enzymes such as glutathione peroxidase, which is known as an endogenous antioxidant enzyme and thioredoxin reeducate (TR) that catalyzes the NADPH- dependent reduction. TR is a major redox protein for many enzymes/transcription factors. The level of Se in soil varies with type, quality and organic contents. Plants absorb Se from soil but its absorption by plants is affected by chemical and physical properties of the soil. In this review, we briefly describe the nature and types of selenoproteins, sources of Se in environment and the different mechanisms by which Se controls redox balance and immune function. Furthermore, we also describe role of selenium in health and diseases.