Question

I'm studying biochemistry from Kaplan's book. In it, I found the following paragraph in the topic on glucose metabolism: GLUT 2, a low-affinity transporter, is in hepatocytes. After a meal, portal blood from the intestine is rich in glucose. GLUT 2 captures the excess glucose primarily for storage. When the glucose concentration drops below the Km for the transporter, much of the remainder leaves the liver and enters the peripheral circulation.

A similar question has already been here, but it didn't help me find an understanding of this. How can we explain that glucose at its concentration less than a Km for the transporter enters the peripheral circulation? Why is this related to Km? I understand, that at glucose concentration equal to a Km, V will be equal to half V max. But even at a low concentration, glucose will still bind to the transporter, although not so actively. Correct me if I'm wrong, but I think that transporting glucose into the hepatocytes at a low speed will be energetically unprofitable or because of the speed of blood flow, it will no longer have time to get into the hepatocytes. Please, give your opinion

Answer 1

GLUT 2, a low-affinity transporter in hepatocytes, captures excess glucose for storage when the concentration is high. When the concentration drops below the Km for the transporter, much of the remaining glucose leaves the liver and enters the peripheral circulation. At low concentrations, transporting glucose into hepatocytes at a slow speed is energetically unprofitable and may not be practical due to the speed of blood flow.

Step-by-step explanation:

GLUT 2 is a low-affinity transporter found in hepatocytes. It captures excess glucose for storage when the glucose concentration in the portal blood is high after a meal. However, when the glucose concentration drops below the Km (Michaelis constant) for the transporter, much of the remaining glucose leaves the liver and enters the peripheral circulation. This happens because at concentrations below the Km, the transporter becomes less active in capturing glucose, allowing it to be transported out of the liver.

At low concentrations, glucose can still bind to the transporter, but not as actively compared to higher concentrations. Transporting glucose into hepatocytes at a slow speed would be energetically unprofitable and may not be practical due to the speed of blood flow. The liver needs to efficiently store glucose when it is abundant, but also release it when glucose levels drop to serve other tissues.

Overall, the relationship between glucose concentration and Km is important because it determines the affinity and transport activity of the GLUT 2 transporter in hepatocytes.