GSK3 substrate

This peptide sequence, RRRAAEELDSRAGpSPQL, corresponds to the sequence of the ε subunit of elF2B surrounding Ser⁵⁴⁰, a target of GSK-3 (glycogen synthase kinase 3) phosphorylation, with the addition of a phosphoserine in the 4 position. This phosphoserine allows for more efficient phosphorylation of the second serine in the peptide(K_m=49 µM for GSK-3ß, 83 µM for GSK-3α). Useful in phosphocellulose GSK-3α and -ß assays.