Glucose-6-phosphate phosphohydrolase

Glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9) is a unique enzyme in several respects. It is the only principal... 

Kim Y-J, Nishida H, Pang C-H, Saito T, Sakemi S, Tonai-Kachi H, Yoshikawa N, Van Volkenberg MA, Parker JC, Kojima Y (2002) CJ-21,164, a New D-Glucose-6-phosphate Phosphohydrolase Inhibitor Produced by a Fungus Chloridium sp. J Antibiot 55 121... 

Snoke and Nordlie (82, 83) have extended these studies of Duttera et al. (87) to include PPS-glucose phosphotransferase as well as glucose-6-P phosphohydrolase activity of the enzyme and have also noted essentially parallel progressive losses of both activities concomitant with release of acid-soluble phosphate resulting from phospholipase C action. A partial (fed animals) or total (fasted rats) restoration of both activities was effected by phospholipid supplementation of phospholipase-treated preparations. However, as indicated by detailed studies of catalytic properties of the various preparations, the enzyme was not restored to its... 

Nordlie and Lygre (118, 132) have carried out detailed pH kinetic studies of PPi-glucose phosphotransferase, CDP-glucose phosphotransferase, and glucose-6-P phosphohydrolase activities with partially purified rat liver enzyme preparations, and they have concluded, on the basis of sharp, unit-changes in slopes of Dixon (133) plots of pKm for phosphate substrates vs. pH near 6.5, that enzyme-bound histidine may participate directly in the catalytic process. Values of Km for glucose were unaffected by reaction mixture pH Km values and relative Vmax values calculated for infinite concentrations of all substrates are tabulated in Table IX. 

In contrast to phosphohydrolases, the phosphatase activity of enzymes which non-hydrolytically catalyse the transfer of phosphate groups can be stimulated by vanadate. Vanadate can spontaneously form esters with unphosphorylated substrates such as sugars. These vanadate esters act as alternative substrates for mutases and isomerases, stimulating their phosphatase activity. Examples are phosphoglucomutase, which catalyses the mutation (phosphate shift) between glucose-1-phosphate and glucose-6-phosphate, and phosphoribose isomerase, which catalyses the isomerisation between ribose-5-phosphate and ribulose-5-phosphate.P ]... 

In addition to altering the maximum potential activity of glucose-6-phosphatase, treatment with phospholipase A leads to a reversible increase in the affinity of this enzyme for glucose-6-phosphate (G-6-P), and to differential stabilities in the PPj-glucose phosphotransferase activity and in the PPi- and glucose-6-P-phosphohydrolase activities of the enzyme. All of these activities (equations la, lb, 2, and 3, below) have been shown to be common to one enzyme (cf., Nordlie and Arion, 1964). 

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