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#GLUT4

6 public questions tagged with this topic.

Membrane Transportation

Which GLUT transporter has the lowest affinity for glucose?

GLUT isoforms display divergent Michaelis constants reflecting tissue metabolic roles and sensing. GLUT2 product of SLC2A2 on 3q26 expressed strongly in hepatocyte sinusoidal membrane pancreatic beta cell plasma membrane intestinal basolateral side and kidney tubule exhibits unusually high Km fifteen to twenty millimolar for glucose also transporting fructose galactose low affinity corresponding to lowest affinity among transporters. This high Km enables effective glucose sensor rather than supply line where rate varies roughly linearly across physiological plasma glucose three to fifteen millimolar without early saturation allowing liver to take up proportionally after meals for glycogen synthesis when sugar high and release glucose during fasting via glucose-6-phosphatase. In beta cells low affinity coupled with high Km glucokinase ensures metabolism proportional to blood glucose linking insulin secretion to glycemia via ATP sensitive K+ channel closure. In intestine high capacity efflux of concentrated glucose via basolateral GLUT2 prevents buildup. By contrast GLUT1 and GLUT3 low Km near one and one point five millimolar provide constitutive high affinity uptake ensuring constant brain glucose despite fluctuations and GLUT4 intermediate Km five millimolar regulated by insulin for muscle storage.

Ref: Thorens, Molecular Aspects of Medicine 2015: GLUT2 – Low Affinity Sensor Transporter.

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Membrane Transportation

Which GLUT transporter is insulin-dependent?

GLUT family encoded by SLC2A genes includes fourteen isoforms differing in distribution, affinity and regulation. GLUT4 product of SLC2A4 stands out as only major isoform acutely dependent on insulin via regulated exocytosis. It contains twelve transmembrane helices forming MFS fold with central glucose cavity. Basally most protein sequestered in perinuclear storage vesicles associated with TUG and VAMP2 retained by AS160 GAP keeping Rab proteins GDP-bound. Insulin activates receptor tyrosine kinase, IRS1 phosphorylation, PI3K producing PIP3, recruiting Akt2 which phosphorylates TBC1D1 and TBC1D4 relieving Rab8A, Rab10, Rab14 to GTP driving vesicle translocation, docking via exocyst and fusion via syntaxin4 SNAP23. Exercise also triggers translocation via AMPK and calcium CaMKK independent of insulin. Once inserted, GLUT4 transports glucose by facilitated diffusion Km around 5 mM matching plasma glucose, enabling rapid postprandial uptake into muscle and adipose for glycogen and triglyceride formation, crucial for glucose homeostasis and postmeal glycemic control impaired in diabetes.

Ref: Huang & Czech, Cell Metabolism 2007: GLUT4 – Insulin-Dependent Glucose Transporter.

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Membrane Transportation

Which type of transport is used by the GLUT4 transporter?

Facilitative GLUT transporters use alternating access without ion coupling. GLUT4 encoded by SLC2A4 is insulin-responsive isoform in skeletal, cardiac muscle and adipose, handling major postprandial glucose disposal. In basal fasting state most GLUT4 sequestered in storage vesicles containing IRAP, sortilin, LRP1 and VAMP2 retained by TUG tether and AS160 GAP keeping Rabs GDP-bound. Insulin triggers receptor tyrosine autophosphorylation, IRS recruitment, PI3K activation producing PIP3 recruiting Akt2 which phosphorylates AS160 relieving Rab8A, Rab10, Rab14 inhibition, mobilizing vesicles along actin tracks to plasma membrane increasing surface density twentyfold within minutes. Once inserted, GLUT4 works as uniporter moving D-glucose down gradient without Na+ coupling or ATP, stereospecific, saturable Km near 5 mM close to plasma glucose, inhibited by cytochalasin B. Entry followed by hexokinase II phosphorylation trapping glucose for glycogen synthesis. Insulin resistance in type 2 diabetes impairs translocation despite preserved total protein due to defective Akt signaling and lipid-induced serine phosphorylation. Recruitment also involves myosin motors and actin remodeling that facilitate vesicle movement toward cortex.

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: GLUT4 and Facilitated Diffusion.

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Cell Signaling ELR Pathways - I

Activation of which small GTPase helps vesicle fusion in GLUT4 transport?

RALA, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling ELR Pathways - I

Basal GLUT4 vesicles are tethered by which protein?

TUG, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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Cell Signaling ELR Pathways - I

Which glucose transporter is insulin responsive?

GLUT4, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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