DL-O-Phosphoserine a normal metabolite in human biofluid is an ester of serine and phosphoric acid. Serine is one of three amino acid residues that are commonly phosphorylated by kinases during cell signaling in eukaryotes.

Alopecurone A exhibits potent inhibitory activity on MRP1.

[pSer2, pSer5, pSer7]-CTD is a substrate for CDK7(cyclin-dependent protein kinase), a phosphorylated polypeptide at ser2, ser5, and ser7 of RNA polymerase II carboxyl terminus (CTD).