31P nuclear magnetic resonance studies of glycogen phosphorylase from rabbit skeletal muscle: ionization states of pyridoxal 5'-phosphate.
31P nuclear magnetic resonance (NMR) at 72.8 MHZ has been used to study glycogen phosphorylase from rabbit muscle (1,4-alpha-D-glucan:orthophosphate alpha-glucosyltransferase, EC 2.4.1.1) at concentrations as low as 25 mg/ml, using a WH-180 wide-bore superconducting spectrometer. The use of a thio analogue for 5'-AMP and arsenate for inorganic phosphate allowed the observation of three distinct forms of enzyme-bound pyridoxal 5'-phosphate at --0.2 ppm (Form I), --2 to --3 ppm (Form II), and --3.5 ppm (Form III) relative to triethylphosphate. Conversion of I to III occurs by activation of phosphorylase either by formation of a ternary complex of phosphorylase b with effector and arsenate or, more efficiently, by direct phosphorylation to give the a form of the enzyme. The ionization state and exposure to solvent of each of the three forms is inferred from the 31P NMR data.
31P nuclear magnetic resonance studies of glycogen phosphorylase from rabbit skeletal muscle: ionization states of pyridoxal 5'-phosphate. 31P nuclear magnetic resonance (NMR) at 72.8 MHZ has been used to study glycogen phosphorylase from rabbit muscle (1,4-alpha-D-glucan:orthophosphate alpha-glucosyltransferase, EC 2.4.1.1) at concentrations as low as 25 mg/ml, using a WH-180 wide-bore superconducting spectrometer. The use of a thio analogue for 5'-AMP and arsenate for inorganic phosphate allowed the observation of three distinct forms of enzyme-bound pyridoxal 5'-phosphate at --0.2 ppm (Form I), --2 to --3 ppm (Form II), and --3.5 ppm (Form III) relative to triethylphosphate. Conversion of I to III occurs by activation of phosphorylase either by formation of a ternary complex of phosphorylase b with effector and arsenate or, more efficiently, by direct phosphorylation to give the a form of the enzyme. The ionization state and exposure to solvent of each of the three forms is inferred from the 31P NMR data.