title: Apparent absence of a translocase in the cerebral glucose-6-phosphatase system.
abstract: In the hepatocyte endoplasmic reticulum, a substrate transporter could provide a means of regulating hydrolysis of glucose-6-phosphate by specifically modulating access of the substrate to the hydrolase. Several characteristics of the cerebral microsomal enzyme suggest that such an hypothesis is untenable in the brain. These are: (a) the inability of the enzyme in either untreated or detergent-disrupted brain microsomes to distinguish between glucose-6-phosphate and mannose-6-phosphate; (b) the close agreement of the apparent Km values for either substrate in intact or disrupted microsomal preparations; (c) the constancy of the latency toward both substrates over a wide concentration range; (d) the inability of nonpenetrating, covalently-linking reagents [e.g., 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)] to affect the accessibility of the hydrolase to its substrate; (e) the absence of a putative transporter polypeptide, such as that of the liver, in experiments where tritiated H2DIDS, polyacrylamide gel electrophoresis, and radioautography are applied to brain microsomes.
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000031:analogs & derivatives; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017920:Antiporters; D001921:Brain / Q000201:enzymology*; D003979:Diazonium Compounds / Q000494:pharmacology; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008297:Male; D008360:Mannosephosphates / Q000378:metabolism; D008861:Microsomes / Q000201:enzymology; D009004:Monosaccharide Transport Proteins; D010770:Phosphotransferases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013425:Sulfanilic Acids / Q000494:pharmacology
chemical_list: D017920:Antiporters; D003979:Diazonium Compounds; D005958:Glucosephosphates; D008360:Mannosephosphates; D009004:Monosaccharide Transport Proteins; C503533:Slc37a4 protein, rat; D013425:Sulfanilic Acids; C111261:glucose 6-phosphate(transporter); D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C027693:mannose-6-phosphate; D019298:Glucose-6-Phosphate; C018564:dihydro-DIDS; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D005952:Glucose-6-Phosphatase; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C000469:diazobenzenesulfonic acid