Sandbox 172: Difference between revisions
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Entry of glucose into a cell is highly dependent on the number of glucose transporters present on the cell surface and the affinity that these specific transporters have for glucose. Expression of these glucose transporter members vary in level and strength different from tissue to tissue. Hexokinase type I has a low Km and therefore a high affinity for glucose. This allows the initiation of glycolysis even when blood glucose levels are relatively low. The inhibition of hexokinase type I is caused by its product, glucose-6-phosphate. This inhibitory step prevents over-consumption of cellular ATP when glucose is not limiting. | Entry of glucose into a cell is highly dependent on the number of glucose transporters present on the cell surface and the affinity that these specific transporters have for glucose. Expression of these glucose transporter members vary in level and strength different from tissue to tissue. Hexokinase type I has a low Km and therefore a high affinity for glucose. This allows the initiation of glycolysis even when blood glucose levels are relatively low. The inhibition of hexokinase type I is caused by its product, glucose-6-phosphate. This inhibitory step prevents over-consumption of cellular ATP when glucose is not limiting. | ||
===Mechanism of Inhibition and Relief=== | ===Mechanism of Inhibition and Relief=== | ||
The activity of hexokinase type I becomes inihibited when glucose-6-phosphate binds to the inactive, N-terminal half of the enzyme. This binding stimulates the inhibition of the active, C-terminal half and as a result, the catalysis of glycolysis becomes stagnant. The presence of orthophosphate relieves the product inhibition by displacing the bound glucose-6-phosphate and binding to the enzyme itself. The N-terminal half then responds differently to the newly bound orthophosphate and evokes an active reaction from the C-terminal half. The ability of the C-terminal half to significantly different between the two possible binding molecules is evident by the presence of ADP-ligated active sites on the hexokinase type I enzyme as well as ADP binding sites on the N-terminal halves. | The activity of hexokinase type I becomes inihibited when glucose-6-phosphate binds to the inactive, N-terminal half of the enzyme. This binding stimulates the inhibition of the active, C-terminal half and as a result, the catalysis of glycolysis becomes stagnant. The presence of orthophosphate relieves the product inhibition by displacing the bound glucose-6-phosphate and binding to the enzyme itself. The N-terminal half then responds differently to the newly bound orthophosphate and evokes an active reaction from the C-terminal half. The ability of the C-terminal half to significantly different between the two possible binding molecules is evident by the presence of ADP-ligated active sites on the hexokinase type I enzyme as well as ADP binding sites on the N-terminal halves. | ||
==References== | ==References== | ||
<references /> | <references /> | ||
<table style="background-color:#ffffc0" cellpadding="8" width="95%" border="0"><tr><td>Please do NOT make changes to this Sandbox until after April 23, 2010. Sandboxes 151-200 are reserved until then for use by the Chemistry 307 class at UNBC taught by Prof. [[User:Andrea Gorrell|Andrea Gorrell]].</td></tr> | <table style="background-color:#ffffc0" cellpadding="8" width="95%" border="0"><tr><td>Please do NOT make changes to this Sandbox until after April 23, 2010. Sandboxes 151-200 are reserved until then for use by the Chemistry 307 class at UNBC taught by Prof. [[User:Andrea Gorrell|Andrea Gorrell]].</td></tr> | ||
