Selenocysteine

Selenocysteine abbreviated as Sec or U; and in older publications as Se-Cys is the 21st protein-building amino acid.Stadtman, Therese 1974. Selenium biochemistry. Science. 183 (4128): 915–22.   It is almost the same as cysteine, but a selenium atom replaces the sulfur atom.

 References 

Category:Amino acids