Neurospora crassa glycogen phosphorylase: Interconversion and kinetic properties of the "active" form

Michael H. Gold, Robert J. Farrand, John P Livoni, Irwin H. Segel

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

Glycogen phosphorylase in cell-free extracts of Neurospora crassa is activated 10- to 15-fold by incubation with MgATP2-. When the MgATP2- is removed, the active form (a form) reverts to the inactive form (b form). The inactivation requires Mg2+ and is inhibited by NaF. The results confirm that Neurospora crassa glycogen phosphorylase exists in two interconvertible forms and strongly suggests that the interconversion is catalyzed by a kinase and phosphatase. The a form was partially purified. The enzyme has a molecular weight of 320,000. Uridine diphosphate glucose is a linear competitive inhibitor with respect to glucose-1-phosphate and a linear non-competitive inhibitor with respect to glycogen. Glucose-6-phosphate is a hyperbolic (partial) noncompetitive inhibitor with respect to all substrates in both directions. The b form of the enzyme in crude cell-free extracts is stimulated 2- to 3-fold by 5′-AMP. As the b form is purified, the 5′-AMP activation is diminished. The molecular weight of the partially purified "b" form was also 320,000.

Original languageEnglish (US)
Pages (from-to)515-527
Number of pages13
JournalArchives of Biochemistry and Biophysics
Volume161
Issue number2
DOIs
StatePublished - 1974

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

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