Recombinant Human Glycogen Phosphorylase is expressed in E. col as the mature form, aa 2-843.

Glycogen Phosphorylase Brain (PYGB) is one of the phosphorylase enzymes (EC2.4.1.1). It breaks up glycogen into glucose subunits. Glycogen is left with one less glucose molecule, and the free glucose molecule is in the form of glucose-1-phosphate. In order to be used for metabolism, it must be converted to glucose-6-phosphateby the enzyme phosphoglucomutase. PYGB can only act on linear chains of glycogen (a 1-4 glycosidic linkage). Its work will immediately come to a halt four residues away from a 1-6 branch (which are exceedingly common in glycogen). In these situations, a debranching enzyme is necessary, which will straighten out the chain in that area. Additionally, an alpha 1-6 glucosidase enzyme is required to break the remaining 1-6 residue that remains in the new linear chain. After all this is done, PYGB can continue. An insulin stimulated enzyme known as phosphoprotein phosphatase (PP-1) inactivates PYGB to prevent glycogen break up.