Selenium
is on the one hand a semi-metal with semiconductor properties, on the other hand it behaves very similarly to sulphur in many reactions and can replace it in many compounds. Selenium-containing amino acids and other compounds derived from the corresponding sulphur-containing compounds are therefore also of biological importance.
To date, more than 20 such selenium-containing proteins or protein subunits are known.
They fulfil important oxidative protective functions in the body's own redox systems:
Glutathione peroxidase, thioredoxin reductase, production of the thyroid hormone T4DNA repair mechanisms, apoptosis in tumour cells