Tungstate: A Potent Inhibitor of Multifunctional Glucose-6-Phosphatase

The insulin-like action of tungstate in diabetic rats (A. Barberàet al.,1994,J. Biol. Chem.269, 20047–20053) prompted us to examine the effects of tungstate on the glucose-6-phosphatase system. Our results indicate that tungstate is a potent inhibitor of glucose-6-phosphatase, with aKiin the 10–25 μ...

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Veröffentlicht in:Archives of biochemistry and biophysics 1998-06, Vol.354 (1), p.125-132
Hauptverfasser: Foster, James D., Young, Shawn E., Brandt, Tami D., Nordlie, Robert C.
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Sprache:eng
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Zusammenfassung:The insulin-like action of tungstate in diabetic rats (A. Barberàet al.,1994,J. Biol. Chem.269, 20047–20053) prompted us to examine the effects of tungstate on the glucose-6-phosphatase system. Our results indicate that tungstate is a potent inhibitor of glucose-6-phosphatase, with aKiin the 10–25 μM range determined with native microsomes and in the 1–7 μM range determined with detergent-treated microsomes. With both preparations, simple linear competitive inhibition was observed versus glucose 6-phosphate (glucose-6-P) as substrate with the glucose-6-P phosphohydrolase activity of the enzyme. Tungstate was a simple linear competitive inhibitor versus carbamyl phosphate (carbamyl-P) and a linear noncompetitive inhibitor versus glucose with the carbamyl-P:glucose phosphotransferase activity of the glucose-6-phosphatase system. These findings, in addition to the observation that tungstate protected the enzyme against thermal inactivation, indicate that tungstate binds with high affinity and competes at the active site of the enzyme where the substrates glucose-6-P and carbamyl-P bind prior to catalysis. Our results suggest that potent inhibition of glucose-6-P hydrolysis by tungstate is likely responsible, at least in part, for the normalization of glycemia and the rebound in hepatic glucose-6-P levels observed in earlier studies in which tungstate exhibited insulin-like action in diabetic rats.
ISSN:0003-9861
1096-0384
DOI:10.1006/abbi.1998.0695