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Which Enzyme Is Crucial for Glucose Homeostasis?

Glucose homeostasis is the balance of insulin and glucagon to maintain blood glucose levels. This is a vital process in the human body, and several enzymes participate in regulating how glucose is metabolized. Among them, glucokinase plays a particularly important role.

Let’s evaluate the given options:

(a) Fructokinase

Fructokinase catalyzes the phosphorylation of fructose to fructose-1-phosphate in the liver. While important in fructose metabolism, it doesn’t play a central role in glucose homeostasis.

(b) Galactokinase

This enzyme is involved in the metabolism of galactose by converting it to galactose-1-phosphate. It is not directly related to blood glucose regulation.

(c) Glucokinase

Correct Answer: Glucokinase is the enzyme that plays a key role in glucose homeostasis. It is primarily found in liver cells and pancreatic β-cells. Glucokinase phosphorylates glucose to glucose-6-phosphate, a crucial step in glycolysis and glycogen synthesis. Unlike hexokinase, glucokinase has a high Km and is not inhibited by glucose-6-phosphate, allowing it to respond effectively to high blood glucose levels. In pancreatic cells, it also serves as a glucose sensor for insulin secretion.

(d) Hexokinase

Hexokinase is present in most tissues and also phosphorylates glucose. However, it operates at low glucose concentrations and is inhibited by glucose-6-phosphate, making it less suited for regulating systemic glucose levels compared to glucokinase.

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Why Glucokinase Is the Master Regulator

• High glucose affinity regulation: Glucokinase is active only when glucose levels are high, helping to remove excess glucose from the bloodstream.

• Pancreatic role: In β-cells, it acts as a glucose sensor that triggers insulin release.

• Liver role: In the liver, it aids in storing glucose as glycogen, thus lowering blood sugar levels.

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Final Answer:

(c) Glucokinase

Glucokinase is the central enzyme in glucose homeostasis, responding dynamically to fluctuations in blood sugar levels.