The phosphorylation level of a particular protein can be determined using a procedure based upon western immunoblotting, with Phos-tag™ reagent present in the SDS-PAGE gel. The Phos-tag™ reagent, supplied in the form of Phos-tag™ acrylamide (Wako Pure Chemical Industries, AAL-107), causes proteins to be resolved both on the basis of size and phosphorylation state. This means that phosphorylated and de-phosphorylated forms of the same protein can be distinguished.