title: Limited proteolysis of glycogen phosphorylase a by subtilisin BPN'.
abstract: The limited proteolysis of rabbit skeletal muscle phosphorylase a was undertaken with subtilisin BPN' immobilized to Sepharose 4B. The effect of substrates, activators and inhibitors of phosphorylase a was investigated by monitoring the changes in phosphorylase activity in the SDS gel electrophoretic pattern and in the 32P-content of 32P-labeled phosphorylase a. Phosphorylase a loses its activity upon subtilisin treatment. All ligands tested protect phosphorylase a activity against subtilisin action, probably by inducing structural changes in the tower loop of the enzyme. Glucose-6-P significantly accelerates [32P]peptide release from phosphorylase a through altering the structure of the N-terminal tail segment. The two subunits of dimeric phosphorylase a are held together by strong interactions--deduced from the correlation of the rate of proteolysis and the disappearance of catalytic activity.
mesh_terms: D000249:Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D004800:Enzymes, Immobilized; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles / Q000201:enzymology*; D010446:Peptide Fragments / Q000378:metabolism; D010762:Phosphorylase a / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism*; D011817:Rabbits; D013381:Subtilisins / Q000494:pharmacology*
chemical_list: D004800:Enzymes, Immobilized; D005958:Glucosephosphates; D046911:Macromolecular Substances; D010446:Peptide Fragments; D000249:Adenosine Monophosphate; D019298:Glucose-6-Phosphate; D010762:Phosphorylase a; D006005:Phosphorylases; D013381:Subtilisins