Official websites use. Share sensitive information only on official, secure websites. Address for reprint requests and other correspondence: S. DevaskarLe Conte Ave. Monosaccharides enter cells by slow translipid bilayer diffusion by rapid, protein-mediated, cation-dependent cotransport and by rapid, protein-mediated equilibrative transport. This review addresses protein-mediated, equilibrative glucose transport catalyzed by GLUT1, the first equilibrative glucose transporter to be identified, purified, and cloned. GLUT1 is a polytopic, membrane-spanning protein that is one of 13 members of the human equilibrative glucose transport protein family. We review GLUT1 catalytic and ligand-binding properties and interpret these behaviors in the context of several putative mechanisms for protein-mediated transport. We conclude that no single model satisfactorily explains GLUT1 behavior. We then review GLUT1 topology, subunit architecture, and oligomeric structure and examine a new model for sugar transport that combines structural and kinetic analyses to satisfactorily reproduce GLUT1 behavior in human erythrocytes. We next review GLUT1 cell biology and the transcriptional and posttranscriptional regulation of GLUT1 expression in the context of development and in response to glucose perturbations and hypoxia in blood-tissue barriers. Emphasis is placed on transgenic GLUT1 overexpression and null mutant model systems, the latter serving as surrogates for the meaning of the name hur GLUT1 deficiency syndrome. Finally, we review the role of GLUT1 in the absence or deficiency of a related isoform, GLUT3, toward establishing the physiological significance of coordination between these two isoforms. Keywords: glucose transport, facilitated diffusion, major facilitator superfamily meaning of the name hur, blood-brain barrier, placenta, diabetes, glucose transporter 1 deficiency syndrome, development. This equilibrative transport process is mediated by a family of sugar transporters called GLUTs. GLUT1 was the first glucose transporter isoform to be identified, purified 66, and cloned 93 and is one of 13 proteins that comprise the human equilibrative glucose transporter family GLUT1 is a membrane-spanning glycoprotein containing 12 transmembrane domains with a single N -glycosylation site, and its gene is located on chromosome 1 1p GLUT1 is expressed at the highest levels in the plasma membranes of proliferating cells forming the early developing embryo, in cells forming the blood-tissue barriers, in human erythrocytes and astrocytes, and in cardiac muscle In addition, GLUT1 transports galactose and ascorbic acid 81 This review examines the catalytic properties, structure, molecular regulation, and physiology of GLUT1. The cytoplasm of most cells equilibrates rapidly with nonmetabolizable extracellular sugars. This process is mediated by sugar transport proteins that catalyze unidirectional sugar uptake and exit, resulting in a net sugar movement down a concentration gradient from high to low sugar concentration. These sugar transport proteins are members of a family of integral membrane proteins called GLUTs that display strong specificity for d -stereoisomers of pentose and hexose monosaccharides adopting the chair configuration of the pyranose ring [e. The availability of human red cells, their high GLUT1 content, and the relative uniformity of meaning of the name hur cell size and surface area has resulted in more than 60 years of sophisticated kinetic analysis of erythrocyte sugar transport. In practical terms, this means that transport measurements are made at very early time points, where the amount of sugar in the cell increases or decreases linearly with time the observed rate of transport is independent of time. This exposes the Achilles heel of sugar transport measurements in human red blood cells. Despite this complexity, glucose transport in human red blood cells has been characterized extensively and has resulted in the development of a number of revealing experimental conditions that permit full characterization of any passive transport system Competitive inhibition studies by Barnett et al. C4 may form a hydrogen bond with GLUT1 because the C4 epimer of d -glucose, d -galactose, has fold lower affinity for GLUT1 than d -glucose. However, an alternative explanation for this is that the nongluco configuration of the sugar hydroxyl group sterically hinders transport. The OH group at C6 seems not to hydrogen bond with GLUT1, and bulky substitutions at this position are tolerated. However, bulky substitutions at C1 are not tolerated. The reverse appears to be true for the sugar exit site. Bulky substitutions at C1 are tolerated, whereas substitutions at C6 are not. A similar pattern is observed for sugar interaction with GLUT4, although the impact of nongluco configurations of hydroxyls is less marked A remaining challenge is to understand the binding requirements at the C1 position of d -glucose. Answers to these questions must await crystallization of the GLUT1- d -glucose complex. Although more complex than anticipated, this behavior does not violate the passive nature of transport. This is caused by the loss of cytoplasmic ATP, which allosterically modifies the catalytic properties of GLUT1 by binding reversibly to a GLUT1 ATP-binding site 10 Simulations of transport reveal important insights into transport function.
Beth-tsur -- "house of a rock," a place in Judah Yes No I didn't get an answer to my question. Privacy Statement. Two types of accelerated exchange or trans -acceleration experiments have been described 78 , Although the various models listed above may represent different physical mechanisms, their King-Altman representations describing the key transport intermediates and their interconversions are identical. The bibliography is a highly analytic one, recording published materials in a wide variety of research languages treating Jewish anthroponymy in the broadest sense from historical, sociological, and linguistic perspectives.
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Society's version of ); (4) meaning even when they did not coincide with the conventional chapters. As a Group with international operations, we focus on the manufacture of high-grade chemical- pharmaceutical specialty products. This review addresses protein-mediated, equilibrative glucose transport catalyzed by GLUT1, the first equilibrative glucose transporter to be identified. name of "Others" (usually referring to the. The name "Immer" is derived from a Hebrew root meaning "to speak" or "to utter," which is fitting given the family's priestly duties involving the spoken.Hitchcock's Bible Names Dictionary Zur stone; rock; that besieges Smith's Bible Dictionary Zur a rock. Offices Worlwide. Availability: Published ISBN: Publication: 30 Aug Editor: David L. This may serve to inhibit further glucose uptake when sufficient intracellular glucose is available to saturate hexokinase. Carruthers is supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK and DK These embryos at e13 revealed morphological abnormalities consisting of a small size, lack of eyes, diminutive rostral embryonic pole, and overall developmental delay vs. Product Details Publisher: Brill Language: English Pages: x, pp. Investigators have employed endometrial stromal cells in both mouse and human and observed that a fine balance has to be struck between the two sex steroids, namely progesterone and estrogen. Anthony Carruthers Anthony Carruthers 1 Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts; and. The perineurium and the vascular endothelium together form the blood-nerve barrier, and both are rich in GLUT1. Ezra ; Nehemiah Easton's Bible Dictionary Talkative. Nehemiah lists the "sons of Immer" among the priests who settled in Jerusalem, indicating their continued role in the religious life of the community. Find articles by Sherin U Devaskar. Steady-state kinetic studies allow the observer to build models that describe the intermediates e. Thou, who Art Three in Unity. Topical Encyclopedia. Further spontaneous seizures were observed along with a decline in brain glucose uptake, as observed with positron emission tomography. Thus, glucose-depleted red cells emerging from glucose-consuming organs such as the brain or placenta are more readily refilled upon reentering glucose-rich circulation. Nehemiah The children of Immer , one thousand fifty-two. This exposes the Achilles heel of sugar transport measurements in human red blood cells. Find articles by Amit Ganguly. Pashhur is mentioned in Jeremiah , where he is described as "the priest, the son of Immer, the chief officer in the house of the LORD. Homology-modeled LacY structure using GlpT as a template approximates transporter topology and architecture but less successfully reproduces the spatial arrangement of amino residues involved in substrate binding to LacY Am J Physiol Endocrinol Metab. C : The GLUT1 model adapted from Fig. The net result is a complex simultaneously presenting at least two exofacial and two endofacial ligand-binding sites 25 , 41 ,
