Glucose Transport and Glucose 6-Phosphate Hydrolysis in Intact Rat Liver Microsomes (∗)

Glucose transport was investigated in rat liver microsomes in relation to glucose 6-phosphatase (Glu-6-Pase) activity using a fast sampling, rapid filtration apparatus. 1) The rapid phase in tracer uptake and the burst phase in glucose 6-phosphate (Glu-6-P) hydrolysis appear synchronous, while the s...

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Bibliographic Details
Published in:The Journal of biological chemistry 1995-09, Vol.270 (36), p.21092-21097
Main Authors: St-Denis, Jean-François, Berteloot, Alfred, Vidal, Hubert, Annabi, Borhane, van de Werve, Gérald
Format: Article
Language:English
Subjects:
Animals
Biological Transport
Glucose - metabolism
Glucose-6-Phosphatase - metabolism
Glucose-6-Phosphate
Glucosephosphates - metabolism
Half-Life
Hydrolysis
Isotopes
Kinetics
Male
Microsomes, Liver - drug effects
Microsomes, Liver - enzymology
Microsomes, Liver - metabolism
Rats
Rats, Wistar
Vanadates - pharmacology
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Summary:Glucose transport was investigated in rat liver microsomes in relation to glucose 6-phosphatase (Glu-6-Pase) activity using a fast sampling, rapid filtration apparatus. 1) The rapid phase in tracer uptake and the burst phase in glucose 6-phosphate (Glu-6-P) hydrolysis appear synchronous, while the slow phase of glucose accumulation occurs during the steady-state phase of glucose production. 2) [14C]Glucose efflux from preloaded microsomes can be observed upon addition of either cold Glu-6-P or Glu-6-Pase inhibitors, but not cold glucose. 3) Similar steady-state levels of intramicrosomal glucose are observed under symmetrical conditions of Glu-6-P or vanadate concentrations during influx and efflux experiments, and those levels are directly proportional to Glu-6-Pase activity. 4) The rates of both glucose influx and efflux are characterized by t values that are independent of Glu-6-P concentrations. 5) Glucose efflux in the presence of saturating concentrations of vanadate was not blocked by 1 mM phloretin, and the initial rates of efflux appear directly proportional to intravesicular glucose concentrations. 6) It is concluded that glucose influx into microsomes is tightly linked to Glu-6-Pase activity, while glucose efflux may occur independent of hydrolysis, so that microsomal glucose transport appears unidirectional even though it can be accounted for by diffusion only over the accessible range of sugar concentrations.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.270.36.21092