Question

Why is it important that Glut2, which is abundant in pancreas beta cells, has a Km for glucose at 15 mM, whilst Glut3 in neurons has a Km 1.5 mM?

Answer 1

Ans:-

concept:- Km value is inversely proportional to affinity of enzyme / channel for substrate.

Km is the concentration of substrate which permits the enzyme/channel to achieve half Vmax. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax."

Now PANCREASE have glut 2 receptor which have high Km value because if glut 2 receptor of PANCREASE is activated it will result in release of insulin. Which will cause influx of glucose inside the cell.

As we know that neuron use only glucose as soul source of energy so glut 3 which is present in neuron have low km i.e high afinity for glucose uptake even at low concentrations of glucose , so that even if concentration of glucose is low in blood then also neurons will uptake the blood glucose.

But if glucose conc is low then pancreatic glut 2 will not be activated and it will not promote uptake of glucose by other cell (via insuline) hence more glucose will be left in the blood for neurons.