Rabbit muscle glycogen-bound phosphoprotein phosphatases

Substrate specificities and effects of inhibitor-1

Balwant S. Khatra, Thomas Soderling

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

A phosphoprotein phosphatase which has an apparent molecular weight of 240,000 was partially purified (500-fold) from the glycogen-protein complex of rabbit skeletal muscle. The enzyme exhibited broad substrate specificity as it dephosphorylated phosphorylase, phosphohistones, glycogen synthase, phosphorylase kinase, regulatory subunit of cAMP-dependent protein kinase, and phosphatase inhibitor 1. The phosphatase showed high specificity towards dephosphorylation of the β-subunit of phosphorylase kinase and site 2 of glycogen synthase. With the latter substrate, the presence of phosphate in sites 1a and 1b decreased the apparent Vmax, perhaps by inhibiting the dephosphorylation of site 2. The phosphorylated form of inhibitor 1 did not significantly inhibit this high-molecular-weight phosphatase. However, an inhibitor 1-sensitive phosphatase activity could be derived from this preparation by limited trypsinization. Furthermore, greater than 70% of the phosphatase activity in skeletal muscle extracts and in the glycogen-protein complex was insensitive to inhibitor 1. Limited trypsinization of each fraction obtained from the phosphatase purification increased the total activity (1.5- to 2-fold) and converted the enzyme into a form which was inhibited by inhibitor 1. The results suggest that inhibitor 1-sensitive phosphatase may be a proteolyzed enzyme.

Original languageEnglish (US)
Pages (from-to)39-51
Number of pages13
JournalArchives of Biochemistry and Biophysics
Volume227
Issue number1
DOIs
StatePublished - 1983
Externally publishedYes

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Phosphoprotein Phosphatases
Substrate Specificity
Glycogen
Phosphoric Monoester Hydrolases
Muscle
Phosphorylase Kinase
Rabbits
Muscles
Substrates
Glycogen Synthase
Skeletal Muscle
Enzymes
Molecular Weight
Glycogen Synthase Kinases
Phosphorylases
Protein Kinase Inhibitors
Cyclic AMP-Dependent Protein Kinases
Molecular weight
Proteins
Phosphates

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

Cite this

Rabbit muscle glycogen-bound phosphoprotein phosphatases : Substrate specificities and effects of inhibitor-1. / Khatra, Balwant S.; Soderling, Thomas.

In: Archives of Biochemistry and Biophysics, Vol. 227, No. 1, 1983, p. 39-51.

Research output: Contribution to journalArticle

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AB - A phosphoprotein phosphatase which has an apparent molecular weight of 240,000 was partially purified (500-fold) from the glycogen-protein complex of rabbit skeletal muscle. The enzyme exhibited broad substrate specificity as it dephosphorylated phosphorylase, phosphohistones, glycogen synthase, phosphorylase kinase, regulatory subunit of cAMP-dependent protein kinase, and phosphatase inhibitor 1. The phosphatase showed high specificity towards dephosphorylation of the β-subunit of phosphorylase kinase and site 2 of glycogen synthase. With the latter substrate, the presence of phosphate in sites 1a and 1b decreased the apparent Vmax, perhaps by inhibiting the dephosphorylation of site 2. The phosphorylated form of inhibitor 1 did not significantly inhibit this high-molecular-weight phosphatase. However, an inhibitor 1-sensitive phosphatase activity could be derived from this preparation by limited trypsinization. Furthermore, greater than 70% of the phosphatase activity in skeletal muscle extracts and in the glycogen-protein complex was insensitive to inhibitor 1. Limited trypsinization of each fraction obtained from the phosphatase purification increased the total activity (1.5- to 2-fold) and converted the enzyme into a form which was inhibited by inhibitor 1. The results suggest that inhibitor 1-sensitive phosphatase may be a proteolyzed enzyme.

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