title: Interactions at the active site of glycogen phosphorylase b. A new laser probe.
abstract: The flash excitation of the pyridoxal 5'-phosphate cofactor of glycogen phosphorylase b by an ultraviolet laser produces a transient state from a proton transfer of the bound cofactor. The rate of decay of this transient state is sensitive to the ionization state of the cofactor. This proved a useful probe for the ionization state of the 5'-phosphate group of the cofactor on the binding by the enzyme of various substrates. The decay rate data show, for the binding of glucose 1-phosphate, a partially negative 5'-HPO4- and evidence for a PO4-PO4 interaction. The data is interpreted in terms of a dynamic shift of substrates at the active site.
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005958:Glucosephosphates / Q000378:metabolism; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D010763:Phosphorylase b / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism*; D011732:Pyridoxal Phosphate / Q000378:metabolism; D011817:Rabbits; D013053:Spectrophotometry
chemical_list: D005958:Glucosephosphates; D000249:Adenosine Monophosphate; D011732:Pyridoxal Phosphate; C031590:glucose-1-phosphate; D010763:Phosphorylase b; D006005:Phosphorylases