Response of rat liver glutaminase to pH, ammonium, and citrate. Possible regulatory role of glutaminase in ureagenesis

L. I. Szweda, D. E. Atkinson

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Liver glutaminase is stimulated by an increase in NH4+ concentration and NH4+ is an absolute requirement for activity at approximate physiological concentrations of phosphate and glutamine. Increases in the concentration of NH4+ cannot, however, overcome the inhibitory effect of a decrease in pH. In addition, the concentration of NH4+ required for half-maximal rate decreases as pH increases. This decrease is the result of two factors: a direct effect of pH on the apparent affinity of the enzyme for NH4+, and an indirect effect of pH brough about by an increase in the apparent affinity of the enzyme for phosphate which results in a further decrease in the M0.5 for NH4a+. In addition, liver glutaminase responds strongly to the concentration of citrate over a physiologically relevant range at approximate physiological concentrations of NH4+, phosphate, and glutamine. An increase in citrate concentration stimulates glutaminase by increasing the affinity of the enzyme for glutamine. The apparent affinity of the enzyme for citrate increases as pH increases. The strong response of liver glutaminase to pH, NH4+, and citrate and the fact that the hydrolysis of glutamine can supply metabolites and effectors for urea synthesis suggest a possible regulatory role of glutaminase in ureagenesis.

Original languageEnglish (US)
Pages (from-to)20869-20873
Number of pages5
JournalJournal of Biological Chemistry
Volume265
Issue number34
StatePublished - Dec 1 1990

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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