RRADDSDDDDD (60537-1) is a selective casein kinase (CK) II substrate. It is not phosphorylated by casein kinase I. In the presence of 150 mM NaCl, CK2 has linear kinetics for the native substrate RRRDDDSDDD with an apparent Km of 60 mM. CK2 displayed biphasic kinetics for the peptide substrate when assayed in the absence of added NaCl.
Ref: Humrich, J. et al. J. Biol. Chem. 278, 4474 (2003); Tiganis, T. et al. Arch. Biochem. Biophys. 325, 289 (1996). Marin, O. et al. Biochem. Biophys. Res. Commun. 198, 898 (1994).