GLUCOSE TRANSPORTERS
153 بار بازدید -
2 سال پیش
-
@vipsbiochemistry5796 Glucose
@vipsbiochemistry5796
Glucose is a large molecule, and polar also hence will not get past the hydrophobic core of the plasma membrane and cannot be transported across the plasma membrane by simple diffusion. Glucose transporters are a wide group of membrane proteins that facilitate the transport of glucose across the plasma membrane,, down its concentration gradient by process of passive facilitated diffusion. Its an example for uniport transporter mechanism also in that only one type of molecule is transported and that too in one direction only.
GLUTs are integral membrane proteins that contain 12 transmembrane-spanning helices with both the amino and carboxyl termini exposed on the cytoplasmic side of the plasma membrane. These transport glucose and related hexoses also. GLUT family of proteins are like isoenzymes in that they differ slightly in their amino acid composition but do the same function of transporting glucose but with slightly different properties. Because glucose is a vital source of energy for all life, these transporters are present in all phyla and is found in most mammalian cells.
Binding of glucose to one site provokes a conformational change associated with transport, and releases glucose to the other side of the membrane. This actually allow our different tissues to meet their varying needs. There are at least 14 GLUT s but here, we will concentrate on the main 5 of them.
GLUT 1 in all cells of the body and it is responsible for the basal glucose uptake of the body. Km value of GLUT 1 is 1mM which is much less than the normal blood glucose level of 5mM and which means they have high affinity for glucose and hence glucose enters these cells easily.
GLUT 3 is present in very high numbers in brain and neurons and is having the same Km value of 1mM as GLUT 1. As we know the chief energy fuel of brain is Glucose and so the transporter should have very high affinity for glucose
GLUT 2 is having a very high Km value of 17 mM which means that they have a very low affinity for binding glucose which is rather understandable with their positioning, because they are concentrated on liver and beta cells of pancreases. In these tissues glucose entry needed to be allowed only when the available glucose in blood is sufficiently high especially like after a meal. Here liver can start to store glucose while beta cells will be induced for production of insulin when the blood level of glucose is more than the upper normal level. Hence the high Km value of GLUT2 is highly significant in these tissues.
GLUT 4 is concentrated in skeletal muscle and adipose tissue and has a Km value of 5mM. Here it can be specially seen that the GLUT 4 is expressed in higher amounts in response to insulin and this further helps to bring down the level of glucose in the blood to normalcy after a carbohydrate meal in addition to the glucose being taken up by liver and pancreatic cells.
GLUT 5 is having the function of taking fructose mainly from the intestine
So here we can see that the presence of GLUT isozymes actually fine tune the glucose metabolic orchestra of different tissues in the body in this manner.
Glucose is a large molecule, and polar also hence will not get past the hydrophobic core of the plasma membrane and cannot be transported across the plasma membrane by simple diffusion. Glucose transporters are a wide group of membrane proteins that facilitate the transport of glucose across the plasma membrane,, down its concentration gradient by process of passive facilitated diffusion. Its an example for uniport transporter mechanism also in that only one type of molecule is transported and that too in one direction only.
GLUTs are integral membrane proteins that contain 12 transmembrane-spanning helices with both the amino and carboxyl termini exposed on the cytoplasmic side of the plasma membrane. These transport glucose and related hexoses also. GLUT family of proteins are like isoenzymes in that they differ slightly in their amino acid composition but do the same function of transporting glucose but with slightly different properties. Because glucose is a vital source of energy for all life, these transporters are present in all phyla and is found in most mammalian cells.
Binding of glucose to one site provokes a conformational change associated with transport, and releases glucose to the other side of the membrane. This actually allow our different tissues to meet their varying needs. There are at least 14 GLUT s but here, we will concentrate on the main 5 of them.
GLUT 1 in all cells of the body and it is responsible for the basal glucose uptake of the body. Km value of GLUT 1 is 1mM which is much less than the normal blood glucose level of 5mM and which means they have high affinity for glucose and hence glucose enters these cells easily.
GLUT 3 is present in very high numbers in brain and neurons and is having the same Km value of 1mM as GLUT 1. As we know the chief energy fuel of brain is Glucose and so the transporter should have very high affinity for glucose
GLUT 2 is having a very high Km value of 17 mM which means that they have a very low affinity for binding glucose which is rather understandable with their positioning, because they are concentrated on liver and beta cells of pancreases. In these tissues glucose entry needed to be allowed only when the available glucose in blood is sufficiently high especially like after a meal. Here liver can start to store glucose while beta cells will be induced for production of insulin when the blood level of glucose is more than the upper normal level. Hence the high Km value of GLUT2 is highly significant in these tissues.
GLUT 4 is concentrated in skeletal muscle and adipose tissue and has a Km value of 5mM. Here it can be specially seen that the GLUT 4 is expressed in higher amounts in response to insulin and this further helps to bring down the level of glucose in the blood to normalcy after a carbohydrate meal in addition to the glucose being taken up by liver and pancreatic cells.
GLUT 5 is having the function of taking fructose mainly from the intestine
So here we can see that the presence of GLUT isozymes actually fine tune the glucose metabolic orchestra of different tissues in the body in this manner.
2 سال پیش
در تاریخ 1401/04/30 منتشر شده
است.
153
بـار بازدید شده