title: Rat liver glucose-6-phosphatase system: light scattering and chemical characterization.
abstract: Glucose-6-phosphatase is a multicomponent system located in the endoplasmic reticulum, involving both a catalytic subunit (G6PC) and several substrate and product carriers. The glucose-6-phosphate carrier is called G6PT1. Using light scattering, we determined K(D) values for phosphate and glucose transport in rat liver microsomes (45 and 33mM, respectively), G6PT1 K(D) being too low to be estimated by this technique. We provide evidence that phosphate transport may be carried out by an allosteric multisubunit translocase or by two distinct proteins. Using chemical modifications by sulfhydryl reagents with different solubility properties, we conclude that in G6PT1, one thiol group important for activity is facing the cytosol and could be Cys(121) or Cys(362). Moreover, a different glucose-6-phosphate translocase, representing 20% of total glucose-6-phosphate transport and insensitive to N-ethylmaleimide modification, could coexist with liver G6PT1. In the G6PC protein, an accessible thiol group is facing the cytosol and, according to structural predictions, could be Cys(284).
authors.affiliation: Laboratoire Inter-universitaire des Activités Physiques et Sportives, Faculté de Médecine, 28 Place Henri Dunant, 63001, Clermont-Ferrand Cedex, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Clottes
authors.forename: Claire
authors.initials: C
authors.lastname: Middleditch
authors.forename: Ann
authors.initials: A
authors.lastname: Burchell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005033:Ethylmaleimide / Q000494:pharmacology; D005952:Glucose-6-Phosphatase / Q000737:chemistry* / Q000378:metabolism*; D007425:Intracellular Membranes / Q000201:enzymology / Q000648:ultrastructure; D007700:Kinetics; D008027:Light; D008623:Mercaptoethanol / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D051381:Rats; D017208:Rats, Wistar; D012542:Scattering, Radiation; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D008623:Mercaptoethanol; D005952:Glucose-6-Phosphatase; D005033:Ethylmaleimide