Publications

• Characterization of a membrane-regulated sugar phosphate phosphohydrolase from Lactobacillus casei.

  London J., Hausman S.Z., Thompson J.

  One of the key components of the futile xylitol cycle of Lactobacillus casei Cl-16 is a phosphatase which dephosphorylates xylitol 5-phosphate to xylitol prior to the expulsion of the pentitol from cells. This enzyme has been partially purified and characterized. The phosphatase is active against ... >> More

  One of the key components of the futile xylitol cycle of Lactobacillus casei Cl-16 is a phosphatase which dephosphorylates xylitol 5-phosphate to xylitol prior to the expulsion of the pentitol from cells. This enzyme has been partially purified and characterized. The phosphatase is active against a variety of four-, five-, and six-carbon sugars and sugar alcohols phosphorylated at the terminal 4, 5, and 6 positions, respectively, but exhibits little or no affinity for substrates phosphorylated at the C-1 position. The enzyme has an apparent molecular weight of 62,000 and a pH optimum between 5.5 and 6, and it requires a divalent cation (Mg2+) for maximal activity. A single protein band, exhibiting phosphatase activity, was excised from polyacrylamide gels and used to prepare antiphosphatase sera in rabbits. The antiserum was used to detect the enzyme on polyacrylamide gels and to determine the molecular weight of the monomer on sodium dodecyl sulfate-polyacrylamide gels. With a subunit molecular weight of 32,000, the native enzyme appears to be a dimer. Phosphatase activity and substrate specificity are regulated by some component associated with the cytoplasmic membrane. << Less

  J Bacteriol 163:951-956(1985) [PubMed] [EuropePMC]

• Purification of cerebral glucose-6-phosphatase. An enzyme involved in sleep.

  Anchors J.M., Karnovsky M.L.

  An insoluble phosphoprotein of rat brain acquires radioactivity from inorganic phosphate more rapidly during sleep than during wakefulness. It was purified in two ways. The first was solvent delipidation of brain tissue followed by preparative sodium dodecyl sulfate polyacrylamide gel electrophore ... >> More

  An insoluble phosphoprotein of rat brain acquires radioactivity from inorganic phosphate more rapidly during sleep than during wakefulness. It was purified in two ways. The first was solvent delipidation of brain tissue followed by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis. The second was sucrose gradient centrifugation of a brain homogenate to remove myelin, and gel filtration on Sephadex G-100 and adsorption chromatography on DEAE-Sephadex in the presence of sodium deoxycholate. The products were homogeneous within the limits of the analytical methods used. The apparent molecular weight of the phosphoprotein was 28,000 on sodium dodecyl sulfate polyacrylamide gels, but was much higher in the presence of sodium deoxycholate. The protein had a high content of aspartic and glutamic acids compared to basic amino acids. Analysis of a base hydrolysate, as well as studies of the kinetics of hydrolysis, showed that the radioactive phosphorus was attached to histidine. The NH2-terminal residue was identified as isoleucine. The phosphoprotein purified by the second method was enzymatically active. When it was incubated in vitro with a 32P-labeled supernatant fraction from rat brain (and later with glucose [6-32P]phosphate), a radioactive phosphorylated protein intermediate was formed. Exploration of the several enzymatic activities of the preparation indicated close correspondence to those reported for the glucose-6-phosphatases of liver and kidney. Glucose-6-phosphatase activity was found in all parts of the brain in the membranous subcellular fractions of neurons. It was shown to be co-purified with the sleep-related phosphoprotein. This report constitutes, we believe, the first complete purification of glucose-6-phosphatase from any tissue and an instance in which a change in the state of a cerebral enzyme has been linked to a normal change in the physiological state of the brain. << Less

  J Biol Chem 250:6408-6416(1975) [PubMed] [EuropePMC]

• Identification and characterisation of a new human glucose-6-phosphatase isoform.

  Guionie O., Clottes E., Stafford K., Burchell A.

  The liver endoplasmic reticulum glucose-6-phosphatase catalytic subunit (G6PC1) catalyses glucose 6-phosphate hydrolysis during gluconeogenesis and glycogenolysis. The highest glucose-6-phosphatase activities are found in the liver and the kidney; there have been many reports of glucose 6-phosphat ... >> More

  The liver endoplasmic reticulum glucose-6-phosphatase catalytic subunit (G6PC1) catalyses glucose 6-phosphate hydrolysis during gluconeogenesis and glycogenolysis. The highest glucose-6-phosphatase activities are found in the liver and the kidney; there have been many reports of glucose 6-phosphate hydrolysis in other tissues. We cloned a new G6Pase isoform (G6PC3) from human brain encoded by a six-exon gene (chromosome 17q21). G6PC3 protein was able to hydrolyse glucose 6-phosphate in transfected Chinese hamster ovary cells. The optimal pH for glucose 6-phosphate hydrolysis was lower and the K(m) higher relative to G6PC1. G6PC3 preferentially hydrolyzed other substrates including pNPP and 2-deoxy-glucose-6-phosphate compared to the liver enzyme. << Less

  FEBS Lett. 551:159-164(2003) [PubMed] [EuropePMC]

• Enzymatic characterization of the pancreatic islet-specific glucose-6-phosphatase-related protein (IGRP).

  Petrolonis A.J., Yang Q., Tummino P.J., Fish S.M., Prack A.E., Jain S., Parsons T.F., Li P., Dales N.A., Ge L., Langston S.P., Schuller A.G.P., An W.F., Tartaglia L.A., Chen H., Hong S.-B.

  Glucose is the main physiological stimulus for insulin biosynthesis and secretion by pancreatic beta-cells. Glucose-6-phosphatase (G-6-Pase) catalyzes the dephosphorylation of glucose-6-phosphate to glucose, an opposite process to glucose utilization. G-6-Pase activity in pancreatic islets could t ... >> More

  Glucose is the main physiological stimulus for insulin biosynthesis and secretion by pancreatic beta-cells. Glucose-6-phosphatase (G-6-Pase) catalyzes the dephosphorylation of glucose-6-phosphate to glucose, an opposite process to glucose utilization. G-6-Pase activity in pancreatic islets could therefore be an important factor in the control of glucose metabolism and, consequently, of glucose-dependent insulin secretion. While G-6-Pase activity has been shown to be present in pancreatic islets, the gene responsible for this activity has not been conclusively identified. A homolog of liver glucose-6-phosphatase (LG-6-Pase) specifically expressed in islets was described earlier; however, the authors could not demonstrate enzymatic activity for this protein. Here we present evidence that the previously identified islet-specific glucose-6-phosphatase-related protein (IGRP) is indeed the major islet glucose-6-phosphatase. IGRP overexpressed in insect cells possesses enzymatic activity comparable to the previously described G-6-Pase activity in islets. The K(m) and V(max) values determined using glucose-6-phosphate as the substrate were 0.45 mm and 32 nmol/mg/min by malachite green assay, and 0.29 mm and 77 nmol/mg/min by glucose oxidase/peroxidase coupling assay, respectively. High-throughput screening of a small molecule library led to the identification of an active compound that specifically inhibits IGRP enzymatic activity. Interestingly, this inhibitor did not affect LG-6-Pase activity, while conversely LG-6-Pase inhibitors did not affect IGRP activity. These data demonstrate that IGRP is likely the authentic islet-specific glucose-6-phosphatase catalytic subunit, and selective inhibitors to this molecule can be obtained. IGRP inhibitors may be an attractive new approach for the treatment of insulin secretion defects in type 2 diabetes. << Less

  J. Biol. Chem. 279:13976-13983(2004) [PubMed] [EuropePMC]