The reactivity of arginine residues interacting with glucose 1-phosphate in glycogen phosphorylase. A comparison between pyridoxal-reconstituted phosphorylase and the native enzyme.
Modification of pyridoxal-reconstituted phosphorylase b with two arginine-directed reagents, butanedione and [14C]phenylglyoxal, has been investigated and compared with the results obtained on the active and inactive conformations of the native enzyme; the reactivity of the various arginine residues has been directly described using autoradiography of chymotryptic maps derived from [14C]phenylglyoxal-labelled phosphorylase. In the native enzyme this method demonstrates that the same arginine residue (568) is reactive on both activated phosphorylase a and b, non-reactive on inactive forms of phosphorylase and protected by glucose 1-phosphate. Another residue is reactive, but its reactivity does not drastically depend upon phosphorylase conformation; it interacts with glucose 1-phosphate. In the pyridoxal-reconstituted phosphorylase, the residue Arg-568 is reactive. This reactivity does not correlated in a simple manner with the ionisation state of the coenzyme, since it is high when this group is either absent or in a dianionic form, and low when it is monoanionic. The reactivity of Arg-568 rather correlates with the quaternary structure of the enzyme. The protection offered by glucose 1-phosphate, pyrophosphate and phosphite on this pyridoxal-reconstituted phosphorylase also provides information about the relative disposition of the substrate, the coenzyme and this particular arginine residue.
D000818:Animals; D001120:Arginine / Q000302:isolation & purification*; D001345:Autoradiography; D055598:Chemical Phenomena; D002621:Chemistry; D004789:Enzyme Activation; D005958:Glucosephosphates; D010762:Phosphorylase a; D010763:Phosphorylase b / Q000037:antagonists & inhibitors; D006005:Phosphorylases / Q000037:antagonists & inhibitors; D011732:Pyridoxal Phosphate; D011817:Rabbits; D013379:Substrate Specificity
D005958:Glucosephosphates; D011732:Pyridoxal Phosphate; D001120:Arginine; C031590:glucose-1-phosphate; D010762:Phosphorylase a; D010763:Phosphorylase b; D006005:Phosphorylases