Wiktionary
phosphatidylserine
n. (context biochemistry English) A phospholipid containing serine.
Wikipedia
Phosphatidylserine
Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is an important phospholipid membrane component (i.e. component of the cell membrane) which plays a key role in cell cycle signaling, specifically in relationship to apoptosis.