Present in all human tissue, numbers of the carrier protein molecule GLUT-1 are more numerous in red blood vessels, in the protective membrane of the blood vessels in the brain and in fetal tissues. GLUT-1 has a strong affinity for glucose molecules, and ensures that both the brain and red blood cells receive appropriate levels of glucose. GLUT-1 is also able to transport galactose, but is unable to transport fructose.
2. GLUT-2
GLUT-2 has a lower affinity for glucose than GLUT-1. It is present throughout all bodily tissues, with the major expression sites being the liver, kidney, pancreas and small intestine. GLUT-2 is capable of transporting glucose, fructose and galactose. GLUT-2 is most active as a glucose transporter when high levels of glucose are present, such as after food.
3. GLUT-3
The major expression sites of GLUT-3 are the brain, placenta and testes. GLUT-3 has a high affinity for glucose, and is also able to transport galactose, but is unable to carry fructose. GLUT-3 is the primary glucose carrier for neurons or nerve cells.
4. GLUT-4
GLUT-4 is an insulin responsive glucose transporter that has a high affinity for glucose. GLUT-4 only carries glucose. The major expression sites are the cardiac muscle, the skeletal system and adipocyte cells. Adipocyte cells are fat cells specializing in storing energy as fats. GLUT-4 transports glucose molecules into adipocytes. Adipocyte cells and the skeletal system both require insulin as well as a glucose transporter protein to absorb glucose molecules from the bloodstream. Insulin is released from the pancreas which then attaches to receptors on the adipocyte and skeletal cell membranes. As GLUT-4 is an insulin responsive protein, it is alerted to the presence of the insulin bound to the receptors on the cell membrane. The GLUT-4 molecule is then able to transport the glucose molecule across the cell membrane and into the cell.
5. SGLUT-1
SGLUT-1 is a cotransporter molecule, with primary expression sites in the intestinal mucosa and kidneys. The intestinal mucosa is the lining of the large and small intestine which absorbs nutrients. Cotransporter molecules usually carry two different sorts of molecules. SGLUT-1 carries one molecule of either glucose or galactose as well as two sodium ions. SGLUT-1 is unable to carry fructose.
References
Types of Glucose Transporters By Katy Willis, eHow Contributor [online]. available at http://www.ehow.com/list_6869400_types-glucose-transporters.html Accessed October 2, 2013
