Purification and characterization of glycogen phosphorylase B from skeletal muscle of the mullet Liza ramada: amino acid sequence of the phosphorylation site.

1. Skeletal muscle glycogen phosphorylase b has been purified from Liza ramada (mullet). 2. The Mr of the purified enzyme subunit was found to be 97,000. By gel filtration a relative Mr of 190,000 was found. 3. Proteolytic digestion of 32P-phosphorylated mullet phosphorylase gave a [32P]-labelled peptide which is observed to contain Ser, its sequence being -Gln-Ile-Ser-Val-Pro-. 4. During 'in vitro' phosphorylation of mullet phosphorylase, 32P was incorporated in different protein bands resolved by isoelectric focusing. The degree of radioactivity associated with each one changed with the incubation time.