Glucose-6-phosphate transport

The 357-residue mammalian glucose-6-phospha-tase plays an important role in metabolism (Chapter 17). Defects in the enzyme cause a glycogen storage disease (Box 20-D) and severe disruption of metabolism.731 However, the molecular basis of its action is not well-known. Furthermore, the active site of the enzyme is located in the lumen of the endoplasmic reticulum732 and glucose-6-phosphate must pass in through the plasma membrane. An additional glucose-6-phosphate transporter subunit may be required to allow the substrate to leave the cytoplasm.73... 

Leuzzi R, Banhegyi G, Kardon T, Marcolongo P, Capecchi PL, 42. Burger, HJ, Benedetti A, Fulceri R. Inhibition of microsomal glucose-6-phosphate transport in human neutrophils results in apoptosis a potential explanation for neutrophil dysfunction in 43. glycogen storage disease type lb. Blood 2003 101 2381-2387. 

Carnitine translocase deficiency and glucose 6-phosphate transporter deficiency. 

Glucose-6-phosphate transport protein (Tl), which transports glucose-6-phosphate into the lumen of the endoplasmic reticulum ... 

Glucose-6-phosphate transporter in hepatocyte microsomal membrane Phosphate transporter in hepatocyte microsomal membrane... 

Carnitine translocase deficiency and glucose 6-phosphate transporter deficiency. For an explanation, see text. Section 22.5. 

Glucose 6-phosphate is ultimately produced by glycogenolysis in the liver (via glucose 1-phosphate), and it is hydrolyzed via glucose-6-phosphatase to give free glucose and phosphate this enzyme is located inside the endoplasmic reticulum, and a specific glucose 6-phosphate transporter allows its entry into this compartment. 

Amino acid transporters, oligopeptide transporters, glucose transporters, lactic acid transporters, monocarboxylic acid transporters, phosphate transporters, bile acid transporters and other transporters present on the apical membrane of the epithelial cells serve as carriers to facilitate nutrient absorption by the intestine. On the basolateral membrane, amino acid and oligopeptide transporters also exist. Drag moieties possessing similar structures to nutrients that are absorbed by such carriers may also be absorbed in this manner. 

Cellular arsenic uptake in the form of As(V) is mediated via phosphate transporters and in the form of As(III) via glyc-eroporin membrane proteins (Mukhopadhyay et al, 2003) or hexose transporters (Liu etal, 2004) or glucose permease GLUTl (Liu et al, 2006). The best characterized arsenic... 

Foscarnet competitively inhibits Na -Pj cotransport in animal and human kidney proximal tubule brush border membrane vesicles, reversibly inhibiting sodium-dependent phosphate transport [48, 49]. Renal cortical Na-K-ATPase and alkaline phosphatase activity are not inhibited by foscarnet, nor is proline, glucose, succinate, or Na" transport [48,49]. Foscarnet induces isolated phosphaturia without hypophosphatemia in thyroparathyroidectomized rats maintained on a low phosphorus diet, without affecting glomerular filtration rate, urinary adenosine 3 5 -cyclic monophosphate (cAMP) activity, or urinary calcium, sodium or potassium excretion [48,50]. Sodium-Pj cotransport in brush border membrane vesicles from human renal cortex was reported to be even more sensitive to inhibition by foscarnet than in rat renal brush border membrane vesicles [49]. 

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