Further Studies on Glucosamine 6-Phosphate Synthesis by Rat Liver Enzymes

Gryder, Rosa M.; Pogell, Burton M.

doi:10.1016/s0021-9258(19)67904-4

Cited by 34 publications

(2 citation statements)

References 6 publications

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“…L-Glutamine:D-fructose-6-phosphate (F6P) 1 amidotransferase (Gfat) catalyzes the conversion of F6P to glucosamine 6-phosphate (GlcN6P) in conjunction with the hydrolysis of glutamine to glutamate. This reaction is the first and ratelimiting step in the hexosamine biosynthetic pathway (1). Subsequent steps metabolize GlcN6P to the major end product UDP-N-acetylglucosamine (UDP-GlcNAc), which is the essential precursor of glycoproteins and glycolipids in the endoplasmic reticulum and Golgi apparatus.…”

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Identification of a Novel Serine Phosphorylation Site in Human Glutamine:Fructose-6-phosphate Amidotransferase Isoform 1

Roux

Lazereg

et al. 2007

Biochemistry

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Glutamine:fructose-6-phosphate amidotransferase (Gfat) catalyzes the first and rate-limiting step in the hexosamine biosynthetic pathway. The increasing amount of evidence that links excess hexosamine biosynthesis with pathogenic complications of type II diabetes highlights the need to understand the regulation of Gfat. Previous studies showed that eukaryotic Gfat is subjected to feedback inhibition by UDP-N-acetyl-d-glucosamine (UDP-GlcNAc) and to phosphorylation by cAMP-activated protein kinase A (PKA). In this study, overexpression of human Gfat isoform 1 (hGfat1) in insect cells revealed that hGfat1 is phosphorylated in vivo. Using matrix-assisted laser desorption/ionization and electrospray tandem mass spectrometry, we have identified Ser243 as a novel phosphorylation site. Biochemical properties of the wild type and the Ser243Glu mutant of hGfat1 overexpressed in Escherichia coli were compared. Our results provide evidence that phosphorylation at Ser243 stimulates glucosamine 6-phosphate-synthesizing activity, lowers amidohydrolyzing activity in the absence of fructose 6-phosphate (F6P) (glutaminase activity), and lowers Km(F6P) 2-fold, but has no effect on UDP-GlcNAc inhibition. On the basis of the sequence consensus, AMP-activated protein kinase and calcium/calmodulin-dependent kinase II were identified to phosphorylate specifically Ser243 in vitro. Phosphorylation by these two kinases results in an increase of enzymatic activity by 1.4-fold. These findings suggest for the first time that hGfat1 may be regulated by kinases other than PKA.

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Identification of a Novel Serine Phosphorylation Site in Human Glutamine:Fructose-6-phosphate Amidotransferase Isoform 1

Roux

Lazereg

et al. 2007

Biochemistry

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The Amidotransferases

Buchanan¹

1973

Advances in Enzymology - And Related Areas of Molecular Biology

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Biochemistry of growth inhibition by ammonium ions in mammalian cells

Ryll¹,

Valley²,

Wagner³

1994

Biotech & Bioengineering

106

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The intracellular pool of UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine has been shown to act as a central target during the inhibitory action of ammonium ions in vitro cultivated mammalian cell cultures. This pool has been demonstrated to be elevated at the end of a batch cultivation and very quickly as a response to exogenously applied ammonium chloride by using four different cell lines (hybridoma, BHK, CHO, and Ltk(-)929). The amount of enlarged UDP aminohexoses is correlated to the inhibitor concentration and additionally dependent on the cell line. The formation of the UDP sugars is associated with a transient reduction of the UTP pool. Moreover, the quick formation of UDP-GNAc is strictly dependent on the presence of glucose and ammonium. Both metabolites act as biochemical precursors. Additionally, the formation of UDP-GNAc after ammonium application has been shown to increase with an elevated cultivation pH and to be independent of the inhibition of transcription and translation processes. The intracellular amount of UDP-GNAc correlates with the level of growth inhibition in mammalian cell lines. (c) 1994 John Wiley & Sons, Inc.

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Further Studies on Glucosamine 6-Phosphate Synthesis by Rat Liver Enzymes

Cited by 34 publications

References 6 publications

Identification of a Novel Serine Phosphorylation Site in Human Glutamine:Fructose-6-phosphate Amidotransferase Isoform 1

Identification of a Novel Serine Phosphorylation Site in Human Glutamine:Fructose-6-phosphate Amidotransferase Isoform 1

The Amidotransferases

Biochemistry of growth inhibition by ammonium ions in mammalian cells

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