Phosphorylase a is an allosteric inhibitor of the glycogen and microsomal forms of rat hepatic protein phosphatase-1

Susana Alemany, Philip Cohen

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    The dephosphorylation of glycogen synthase by protein phosphatase-1 in hepatic glycogen and microsomes was inhibited by nanomolar concentrations of phosphorylase a. The I50 for phosphorylase a was 1000-fold lower than its Km as a substrate, while tryptic digestion increased the I50 1000-fold without affecting Km. 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.

    Original languageEnglish
    Pages (from-to)194-202
    Number of pages9
    JournalFEBS Letters
    Issue number2
    Publication statusPublished - 31 Mar 1986



    • (Liver)
    • Glycogen synthase
    • Hormonal regulation
    • Microsome
    • Protein phosphatase-1
    • Protein phosphorylation

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