title: Phosphorylation-induced conformational changes in the phosphorylase ab hybrid as revealed by resolution of pyridoxal 5'-phosphate with imidazole citrate and cysteine.
abstract: The accessibility of pyridoxal 5'-phosphates of the phosphorylase ab hybrid to resolution by imidazole citrate and cysteine was studied and compared with that of the b and a forms. Promotion of resolution of phosphorylated forms by raising the temperature or in the presence of glycogen indicates that the resistance of phosphorylase a and ab to resolution at 0 degrees C is due rather to their tetrameric state than their phosphorylation-related active conformation. The pattern of resolution of the ab hybrid was similar to that of the a and differed from that of the b forms in that it occurred at 30 degrees C and 37 degrees C but not at 0 degrees C, moreover, it did not show first-order kinetics. On the other hand, inhibition of resolution by ligands binding to the nucleotide site of phosphorylase reflected an intermediate sensitivity of the ab form between that of the b and a forms. We conclude that partial phosphorylation of phosphorylase b elicits conformational change(s) in both subunits which influence the monomer-monomer interactions and resolution of pyridoxal 5'-phosphates. Resistance of ab hybrid to monomerizing agents as imidazole citrate, comparable to that of other forms, argues for its stability, ruling out its reshuffling into mixtures of phosphorylase b and a.
authors.affiliation: Department of Medical Chemistry, University School of Medicine, Debrecen, Hungary.
authors.forename: G
authors.initials: G
authors.lastname: Vereb
authors.forename: E
authors.initials: E
authors.lastname: Pallagi
authors.forename: P
authors.initials: P
authors.lastname: Gergely
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000818:Animals; D003545:Cysteine / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D006005:Phosphorylases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011487:Protein Conformation; D011732:Pyridoxal Phosphate / Q000378:metabolism*; D011817:Rabbits; D013696:Temperature
chemical_list: D007093:Imidazoles; D008024:Ligands; D000249:Adenosine Monophosphate; D011732:Pyridoxal Phosphate; D006005:Phosphorylases; D003545:Cysteine