Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated. Sulfation was first discovered by Betteheim in bovine fibrinopeptide B in 1954 and later found be present in animals and plants but not in prokaryotes or in yeast.