Response of rat liver glutaminase to magnesium ion

Luke I. Szweda, Daniel E. Atkinson

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

The activity of rat liver glutaminase from sedimented fractions of freeze-thawed mitochondria is strongly affected by variation in the Mg2+ concentration within the approximate physiological range of activators. A rise in the Mg2+ concentration stimulates glutaminase by increasing the apparent affinity of the enzyme for its positive modifier phosphate. With the addition of 4 mM Mg2+ the M0.5 for phosphate activation decreased from 18 to 9.5 mM at pH 7.1, 10 to 5.8 mM at pH 7.4 and 6.4 to 4.0 mM at pH 7.7. The result is an increase in the apparent affinity of the enzyme for glutamine. With the addition of 4 mM Mg2+ the S0.5 of glutaminase for glutamine decreased from 24 to 13 mM at pH 7.1, 14 to 9.6 mM at pH 7.4, and remained unchanged at 8.2 mM at pH 7.7. Since Mg2+ stimulates glutaminase, as does a rise in pH (Szweda, L.I. and Atkinson, D.E. (1989) J. Biol. Chem. 264, 15357-15360), by increasing the apparent affinity of the enzyme for phosphate, it reduces the inhibitory effect of a decrease in pH and/or phosphate concentration over a physiologically relevant range.

Original languageEnglish (US)
Pages (from-to)201-206
Number of pages6
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Volume1041
Issue number2
DOIs
StatePublished - Nov 15 1990

Keywords

  • Liver glutaminase
  • Magnesium ion
  • Phosphate
  • pH

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology

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