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Phosphorylase a is an allosteric inhibitor of the glycogen and microsomal forms of rat hepatic protein phosphatase‐1
Author(s) -
Alemany Susana,
Cohen Philip
Publication year - 1986
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(86)80404-5
Subject(s) - glycogen phosphorylase , phosphorylase kinase , microsome , phosphatase , dephosphorylation , biochemistry , allosteric regulation , chemistry , protein phosphatase 1 , glycogen synthase , glycogen branching enzyme , enzyme , glycogen
The dephosphorylation of glycogen synthase by protein phosphatase‐1 in hepatic glycogen and microsomes was inhibited by nanomolar concentrations of phosphorylase a . The I 50 for phosphorylase a was 1000‐fold lower than its K m as a substrate, while tryptic digestion increased the I 50 1000‐fold without affecting K m . Protein phosphatase‐1 from skeletal muscle and protein phosphatase‐2A from liver were only inhibited at 1000‐fold higher concentrations. Protein phosphatase‐1 became desensitized to phosphorylase a when released from hepatic microsomes, but sensititvity was partially restored by readdition of the solubilized enzyme to the microsomes. The results demonstrate that phosphorylase a is a potent allosteric inhibitor of hepatic protein phosphatase‐1 and suggest that inhibition may be conferred by a novel phosphorylase a ‐binding subunit.