PYGL also known as Glycogen phosphorylase, switches from inactive phosphorylase B to active phosphorylase A by phosphorylation of serine residue 15. Activity of this enzyme is further regulated by multiple allosteric effectors and hormonal controls. The liver isozyme serves the glycemic demands of the body in general while the brain and muscle isozymes supply just those tissues. Recombinant human PYGL, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.