Casein kinase I substrate peptide

This sequence, RRKDLHDDEEDEAMSITA, is derived from inhibitor-2 of protein phosphatase-1 with changes that make it an excellent substrate for casein kinase I (Km=172 µM), while rendering it a poor substrate for casein kinase II.

The addition of two arginyl residues to the amino-terminus allows it to be used in phosphocellulose kinase assays.