Biochemistry I   Spring & Fall Terms

Superimposed R & T States (monomers)     R State only     T State only View these R State structures above: + AMP Original R State

View these T State structures above: + Glucose (Glc) + Glucose-1-phosphate (G-1-P) Original T State + AMP

Muscle Glycogen Phosphorylase (mGP) is a dimer (subunit M_r = 97 kDa). The Backbone structures are shown of the phosphorylated (mGPa) and the unphosphorylated (mGPb) forms with Spacefill models of substrates and effectors:
1. The essential cofactor at the active site, pyridoxal phosphate (PLP), is colored yellow.
2. AMP is colored CPK at the allosteric site.
3. Ser 14 and phospho-Ser 14 are CPK.
Phosphorylation of Ser 14 causes a large reorganization of the N-terminal 20 amino acids (colored white) in which Ser 14 moves about 35 Å to the dimer interface of mGPa. In this form, the fully active enzyme is not affected by AMP, even though it can still bind to the allosteric site.
The unphosphorylated enzyme, mGPb, is subject to allosteric activation by AMP and inhibition by glucose (Glc) and glucose-1-phosphate (G-1-P).