After a carbohydrate-rich meal, when the blood glucose concentration more than doubles, which of the following glucose transporters would be operating closest to its Vmax? A. GLUT4, because its Kt is most similar to normal blood glucose levels. B. GLUT3, because it has a very low Kt, which protects the brain under starvation conditions. C. GLUT2, because it has a very high Kt, which helps regulate insulin production and removal of glucose from the blood. D. GLUT1, because it has a moderately low Kt, which provides a constant flow of glucose into most cells of the body to maintain their basal cellular functions.
Question
After a carbohydrate-rich meal, when the blood glucose concentration more than doubles, which of the following glucose transporters would be operating closest to its Vmax? A. GLUT4, because its Kt is most similar to normal blood glucose levels. B. GLUT3, because it has a very low Kt, which protects the brain under starvation conditions. C. GLUT2, because it has a very high Kt, which helps regulate insulin production and removal of glucose from the blood. D. GLUT1, because it has a moderately low Kt, which provides a constant flow of glucose into most cells of the body to maintain their basal cellular functions.
Solution
The answer is C. GLUT2, because it has a very high Kt, which helps regulate insulin production and removal of glucose from the blood.
Here's why:
Vmax refers to the maximum rate of reaction, or the point at which increasing substrate concentration no longer increases the rate of reaction. This typically occurs when all of the available enzyme (in this case, the glucose transporter) is bound to substrate (in this case, glucose).
GLUT2 has a high Kt, meaning it has a low affinity for glucose. This means it requires a high concentration of glucose to become saturated and operate at its Vmax. After a carbohydrate-rich meal, blood glucose levels would be high, potentially high enough to saturate GLUT2 and cause it to operate at or near its Vmax.
The other transporters, GLUT1, GLUT3, and GLUT4, have lower Kt values, meaning they have higher affinities for glucose. They would become saturated and reach their Vmax at lower glucose concentrations. Therefore, even after a carbohydrate-rich meal, they would not be operating as close to their Vmax as GLUT2.
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