TY - JOUR
T1 - Response of rat liver glutaminase to magnesium ion
AU - Szweda, Luke I.
AU - Atkinson, Daniel E.
N1 - Funding Information:
This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grant DK 36941 and by USPHS National Research Service Award GM 07185.
PY - 1990/11/15
Y1 - 1990/11/15
N2 - 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.
AB - 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.
KW - Liver glutaminase
KW - Magnesium ion
KW - Phosphate
KW - pH
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U2 - 10.1016/0167-4838(90)90066-O
DO - 10.1016/0167-4838(90)90066-O
M3 - Article
C2 - 2265206
AN - SCOPUS:0025155513
SN - 0167-4838
VL - 1041
SP - 201
EP - 206
JO - Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
JF - Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
IS - 2
ER -