Define about Selenoproteins P and W?

The third group comprises of selenoprotein P, an extracellular constituent with multiple selenocysteine molecules. This has an antioxidant role, deactivating free radicals. Selenoprotein W, present in the muscle has a suggested role in muscular degeneration seen in combined selenium and vitamin E deficiency. Selenoprotein W gets reduced during selenium deficiency. Another group of selenium-containing enzymes is the thioredoxin reductases. The selenoenzyme thioredoxin reductase is involved in disposal of the products of oxidative metabolism.

It contains two selenocysteine groups per molecule and is a major component of a redox system with a multiplicity of functions, among which is the capacity to degrade locally excessive and potentially toxic concentrations of peroxide and hydroperoxides likely to induce cell death and tissue atrophy. These selenoproteins catalyze the NADPH-dependent reduction of oxidized thioredoxin. Reduced thioredoxin provides reducing equivalents for various redox- dependent systems, such as, ribonucleotide reductase essential for DNA synthesis, redox regulation of transcription factors. Besides, these proteins have important functions in regulating cell growth and inhibiting apoptosis. The above discussion clearly indicates the importance of selenium in human nutrition. Let us now find out how selenium status can have an impact on our health. We shall begin with the state of deficiency and then discuss the consequences of toxic levels of selenium.