UMass Chan Affiliations
Department of Biochemistry and Molecular PharmacologyDocument Type
Journal ArticlePublication Date
2009-01-05Keywords
Biological TransportMembrane Transport Proteins
Erythrocytes
Glucose Transporter Type 1
membrane transport; erythrocytes; GLUT1
Biochemical Phenomena, Metabolism, and Nutrition
Biochemistry, Biophysics, and Structural Biology
Medical Biophysics
Medical Physiology
Pharmacology, Toxicology and Environmental Health
Metadata
Show full item recordAbstract
Equilibrative sugar uptake in human erythrocytes is characterized by a rapid phase, which equilibrates 66% of the cell water, and by a slow phase, which equilibrates 33% of the cell water. This behavior has been attributed to the preferential transport of beta-sugars by erythrocytes (Leitch JM, Carruthers A. Am J Physiol Cell Physiol 292: C974-C986, 2007). The present study tests this hypothesis. The anomer theory requires that the relative compartment sizes of rapid and slow transport phases are determined by the proportions of beta- and alpha-sugar in aqueous solution. This is observed with d-glucose and 3-O-methylglucose but not with 2-deoxy-d-glucose and d-mannose. The anomer hypothesis predicts that the slow transport phase, which represents alpha-sugar transport, is eliminated when anomerization is accelerated to generate the more rapidly transported beta-sugar. Exogenous, intracellular mutarotase accelerates anomerization but has no effect on transport. The anomer hypothesis requires that transport inhibitors inhibit rapid and slow transport phases equally. This is observed with the endofacial site inhibitor cytochalasin B but not with the exofacial site inhibitors maltose or phloretin, which inhibit only the rapid phase. Direct measurement of alpha- and beta-sugar uptake demonstrates that erythrocytes transport alpha- and beta-sugars with equal avidity. These findings refute the hypothesis that erythrocytes preferentially transport beta-sugars. We demonstrate that biphasic 3-O-methylglucose equilibrium exchange kinetics refute the simple carrier hypothesis for protein-mediated sugar transport but are compatible with a fixed-site transport mechanism regulated by intracellular ATP and cell shape.Source
Am J Physiol Cell Physiol. 2009 Jan;296(1):C151-61. Epub 2008 Nov 5. Link to article on publisher's siteDOI
10.1152/ajpcell.00359.2008Permanent Link to this Item
http://hdl.handle.net/20.500.14038/26118PubMed ID
18987250Related Resources
Link to article in PubMedae974a485f413a2113503eed53cd6c53
10.1152/ajpcell.00359.2008
Scopus Count
Collections
Related items
Showing items related by title, author, creator and subject.
-
Sequence Determinants of GLUT1-mediated Accelerated-exchange Transport: Analysis by Homology-Scanning MutagenesisVollers, Sabrina S.; Carruthers, Anthony (2012-12-14)The class 1 equilibrative glucose transporters GLUT1 and GLUT4 are structurally similar but catalyze distinct modes of transport. GLUT1 exhibits trans-acceleration, in which the presence of intracellular sugar stimulates the rate of unidirectional sugar uptake. GLUT4-mediated uptake is unaffected by intracellular sugar. Using homology-scanning mutagenesis in which domains of GLUT1 are substituted with equivalent domains from GLUT4 and vice versa, we show that GLUT1 transmembrane domain 6 is both necessary and sufficient for trans-acceleration. This region is not directly involved in GLUT1 binding of substrate or inhibitors. Rather, transmembrane domain 6 is part of two putative scaffold domains, which coordinate membrane-spanning amphipathic helices that form the sugar translocation pore. We propose that GLUT1 transmembrane domain 6 restrains import when intracellular sugar is absent by slowing transport-associated conformational changes.
-
Atg6 is required for multiple vesicle trafficking pathways and hematopoiesis in DrosophilaShravage, Bhupendra V.; Hill, Jahda H.; Powers, Christine M.; Wu, Louisa; Baehrecke, Eric H. (2013-03-15)Atg6 (beclin 1 in mammals) is a core component of the Vps34 complex that is required for autophagy. Beclin 1 (Becn1) functions as a tumor suppressor, and Becn1(+/-) tumors in mice possess elevated cell stress and p62 levels, altered NF-kappaB signaling and genome instability. The tumor suppressor function of Becn1 has been attributed to its role in autophagy, and the potential functions of Atg6/Becn1 in other vesicle trafficking pathways for tumor development have not been considered. Here, we generate Atg6 mutant Drosophila and demonstrate that Atg6 is essential for autophagy, endocytosis and protein secretion. By contrast, the core autophagy gene Atg1 is required for autophagy and protein secretion, but it is not required for endocytosis. Unlike null mutants of other core autophagy genes, all Atg6 mutant animals possess blood cell masses. Atg6 mutants have enlarged lymph glands (the hematopoietic organ in Drosophila), possess elevated blood cell numbers, and the formation of melanotic blood cell masses in these mutants is not suppressed by mutations in either p62 or NFkappaB genes. Thus, like mammals, altered Atg6 function in flies causes hematopoietic abnormalities and lethality, and our data indicate that this is due to defects in multiple membrane trafficking processes.
-
Insulin action on GLUT4 traffic visualized in single 3T3-l1 adipocytes by using ultra-fast microscopyPatki, Varsha; Buxton, Joanne M.; Chawla, Anil; Lifshitz, Lawrence M.; Fogarty, Kevin E.; Carrington, Walter A.; Tuft, Richard A.; Corvera, Silvia (2001-02-13)A novel imaging technology, high-speed microscopy, has been used to visualize the process of GLUT4 translocation in response to insulin in single 3T3-L1 adipocytes. A key advantage of this technology is that it requires extremely low light exposure times, allowing the quasi-continuous capture of information over 20-30 min without photobleaching or photodamage. The half-time for the accumulation of GLUT4-eGFP (enhanced green fluorescent protein) at the plasma membrane in a single cell was found to be of 5-7 min at 37 degrees C. This half-time is substantially longer than that of exocytic vesicle fusion in neuroendocrine cells, suggesting that additional regulatory mechanisms are involved in the stimulation of GLUT4 translocation by insulin. Analysis of four-dimensional images (3-D over time) revealed that, in response to insulin, GLUT4-eGFP-enriched vesicles rapidly travel from the juxtanuclear region to the plasma membrane. In nontransfected adipocytes, impairment of microtubule and actin filament function inhibited insulin-stimulated glucose transport by 70 and 50%, respectively. When both filament systems were impaired insulin-stimulated glucose transport was completely inhibited. Taken together, the data suggest that the regulation of long-range motility of GLUT4-containing vesicles through the interaction with microtubule- and actin-based cytoskeletal networks plays an important role in the overall effect of insulin on GLUT4 translocation.