Active site peptides from glycogen phosphorylase

The isolation and sequence of active site peptides from glycogen phosphorylase b is described. These cysteine peptides become exposed to preferential labeling upon removal of pyridoxal 5′-phosphate (PLP) from the enzyme and they have the sequence Ala-Cys, Asx-Ala-Cys-Asp and Asx-Glx-Lys-Cys-Gly-Gly. The first two of these peptides appear to be derived from the PLP binding site of phosphorylase.