Most mammalian cells transport glucose through a family of membrane proteins known as glucose transporters.
Molecular cloning of these glucose transporters has identified a family of closely related genes that encodes at least 7 proteins (Glut-1 to Glut-7, MW.
40-60kD) and Sodium glucose co-transporter-1 (SGLT-1, 662 amino acids; ~75kD).
Individual member of this family have identical predicted secondary structures with 12 transmembrane domains.
Both N and c-termini are predicted to be cytoplasmic.
Most differences in sequence homology exist within the four hydrophilic domains that may play a role in tissue-specific targeting.
Glut isoform differ in their tissue expression, substrate specificity and kinetic characteristics.
Glut-1 mediates glucose transport into red cells, and throughout the blood brain barrier, and supply glucose to most cells.
Glut-2 provides glucose to the liver and pancreatic cells.
Glut-3 is the main transporter in neurons, whereas Glut-4 is primarily expressed in muscle and adipose tissue and regulated by insulin.
Glut-5 transports fructose in intestine and testis.
Glut-6/SLC2A6, originally described as glut-9 has been reassigned as Glut-6.
Glut-6 (human 507 aa; ~ 48kD; chromosome 9q34) is most closely related to Glut-8 (~45% homology).
It is highly expressed in brain, spleen, and peripheral leukocytes.
Glut-7, expressed in liver and other gluconeogenic tissues, mediates glucose flux across endoplasmic reticulum membrane.
Glut-8 is found in adult testis and placenta.
Human Glut-9 is expressed in spleen, peripheral leukocytes and brain.
Human Glut-10 (541 aa, chromosome 20q13.1; ~30-35% homology with Glut-3 and Glut-8) has been identified as a candidate gene for NIDDM susceptibility.
It is widely expressed with highest levels in liver and pancreas.
Glut-11 (496 aa, chromosome 22q11.2; ~41% identity with Glut-5) is expressed in heart and skeletal muscle.
Glut-12 (human 617 aa, monkey 621 aa;~ 50kD; ~30% homology with Glut-4 and 40% with Glut-10) is expressed in skeletal muscle, adipose tissue, and small intestine .
Glut-13 or proton myo-inositol transporter (HMIT; human 629 aa, rat 618 aa, ~75-90kD/67kD protein) is highly expressed in glial cells and some neurons.
Glut-13 transport activity was specific for myo-inositol.
Rat HMIT is ~35% identical to rat GlutX1.
Applications:Suitable for use in ELISA.
Western Blot, though not tested, may potentially be used as an application.
