Passage
Diabetic nephropathy (kidney disease) is characterized in part by a significant decrease in the glomerular filtration rate. Podocytes are differentiated cells that surround the glomerular capillaries and counteract the pressure of blood filtration. Hyperglycemia (elevated blood glucose) and capillary hypertension (high blood pressure) , both of which are common in diabetic patients, can subject podocytes to mechanical stress. This mechanical stress has been shown to regulate glucose uptake by podocytes, possibly by altering the production of glucose transport (GLUT) proteins.Researchers investigating GLUT2 and GLUT4 expression in rat podocytes measured the impact of mechanical stress on glucose uptake. Cells were grown for 4 hours on membranes exposed to atmospheric (atm) or high air pressure (HP) to mimic mechanical stress. Antibodies specific to GLUT2 and GLUT4 were used to visualize the expression of each under normal glucose (NG) and hyperglycemic (HG) conditions, and to assess the effect of mechanical stress on expression. The uptake of a radiolabeled glucose analogue, [³H]-2-deoxy-D-glucose (3H-2DG) , was then determined. The quantity of 3H-2DG transported by each GLUT protein was directly proportional to the cell surface expression.
Figure 1 Cell surface expression of GLUT transporters in response to mechanical stress and varying glucose concentration.In vivo studies have shown that transport via GLUT2 is noninducible and depends only on extracellular glucose concentrations. However, GLUT4-mediated uptake is induced by insulin binding and occurs under high glucose conditions when insulin is released. The standard K_m values for GLUT2 and GLUT4 are 19.4 and 4.3 mM, respectively, at normal blood glucose levels after a meal (~7.8 mM) . The data shown in Figure 2 represent the combined kinetic properties of both transporters.
Figure 2 Plot of glucose uptake in podocytes with and without mechanical stress.
Adapted from Lewko, B., Bryl, E., Witkowski, J. M., Latawiec, E., Angielski, S., & Stepinski, J. (2005) . Mechanical stress and glucose concentration modulate glucose transport in cultured rat podocytes. Nephrology Dialysis Transplantation, 20(2) , 306-311.
-The drug indinavir inhibits GLUT isoforms noncompetitively. Researchers predict that GLUT4 is significantly more susceptible to indinavir than GLUT2. Which of the following observations would best support their hypothesis?

Question

Passage
Diabetic nephropathy (kidney disease) is characterized in part by a significant decrease in the glomerular filtration rate. Podocytes are differentiated cells that surround the glomerular capillaries and counteract the pressure of blood filtration. Hyperglycemia (elevated blood glucose) and capillary hypertension (high blood pressure) , both of which are common in diabetic patients, can subject podocytes to mechanical stress. This mechanical stress has been shown to regulate glucose uptake by podocytes, possibly by altering the production of glucose transport (GLUT) proteins.Researchers investigating GLUT2 and GLUT4 expression in rat podocytes measured the impact of mechanical stress on glucose uptake. Cells were grown for 4 hours on membranes exposed to atmospheric (atm) or high air pressure (HP) to mimic mechanical stress. Antibodies specific to GLUT2 and GLUT4 were used to visualize the expression of each under normal glucose (NG) and hyperglycemic (HG) conditions, and to assess the effect of mechanical stress on expression. The uptake of a radiolabeled glucose analogue, [³H]-2-deoxy-D-glucose (3H-2DG) , was then determined. The quantity of 3H-2DG transported by each GLUT protein was directly proportional to the cell surface expression.

Figure 1 Cell surface expression of GLUT transporters in response to mechanical stress and varying glucose concentration.In vivo studies have shown that transport via GLUT2 is noninducible and depends only on extracellular glucose concentrations. However, GLUT4-mediated uptake is induced by insulin binding and occurs under high glucose conditions when insulin is released. The standard K_m values for GLUT2 and GLUT4 are 19.4 and 4.3 mM, respectively, at normal blood glucose levels after a meal (~7.8 mM) . The data shown in Figure 2 represent the combined kinetic properties of both transporters.

Figure 2 Plot of glucose uptake in podocytes with and without mechanical stress.
Adapted from Lewko, B., Bryl, E., Witkowski, J. M., Latawiec, E., Angielski, S., & Stepinski, J. (2005) . Mechanical stress and glucose concentration modulate glucose transport in cultured rat podocytes. Nephrology Dialysis Transplantation, 20(2) , 306-311.
-The drug indinavir inhibits GLUT isoforms noncompetitively. Researchers predict that GLUT4 is significantly more susceptible to indinavir than GLUT2. Which of the following observations would best support their hypothesis?

Quizplus · Accepted Answer

11ecba2d_0e83_b598_a3bf_d7bbd7427b68_MD0008_00 Inhibitors are compounds that alter protein activity by changing the reaction rate V_max or the binding affinity K_m of the protein. Based on the information in the question, GLUT transporters are susceptible to noncompetitive inhibition by the drug indinavir. Noncompetitive inhibitors bind to regions other than the active site and have equal affinity for the free protein and the protein-substrate complex. As a result, noncompetitive inhibition causes a decrease in V_max but has no effect on K_m. Although indinavir inhibits both GLUT transporters, researchers predict that indinavir has a greater impact on GLUT4 than on GLUT2. In the presence of the inhibitor, GLUT4 will exhibit a lower V_max value in comparison to GLUT2. Therefore, indinavir decreases the V_max of GLUT4 to a greater extent than the V_max of GLUT2. (Choice A) Indinavir is noncompetitive and binds to both the free GLUT4 transporter and the GLUT4-glucose complex. Only uncompetitive inhibitors bind exclusively to the protein-substrate complex. (Choice B) The inhibitor has a greater effect on GLUT4-mediated glucose uptake than on GLUT2. More glucose will be transported by GLUT2 than by GLUT4. (Choice C) Noncompetitive inhibition does not affect the K_m of an enzymatic reaction, so neither transporter will have a decreased K_m. Educational objective: Noncompetitive inhibitors bind enzymes at sites other than the active site. They bind the free enzyme and the enzyme-substrate complex with equal affinity. This type of inhibition is characterized by a decrease in V_max with no change in the K_m value.

Passage Diabetic Nephropathy (Kidney Disease) Is Characterized in Part by a a Significant