Which enzyme is primarily responsible for the phosphorylation of glucose in the liver?

• A. Phosphofructokinase
• B. Glucokinase
• C. Pyruvate kinase
• D. Mevalonate kinase

Answer: (B)

The enzyme primarily responsible for the phosphorylation of glucose in the liver is glucokinase. Glucokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is the first step in the process of glycolysis as well as in glycogen synthesis. This enzyme is specifically important in the liver because it functions at high Km levels, meaning it has a low affinity for glucose and acts in a capacity that allows the liver to effectively handle high concentrations of glucose, especially after meals. It also plays a crucial role in regulating blood sugar levels by storing excess glucose as glycogen.

Phosphofructokinase, while a key regulatory enzyme in glycolysis, acts later in the pathway and does not initiate glucose phosphorylation. Pyruvate kinase catalyzes the final step of glycolysis, converting phosphoenolpyruvate to pyruvate, but it does not phosphorylate glucose. Mevalonate kinase is involved in the mevalonate pathway, which is unrelated to glucose metabolism. Thus, glucokinase is the enzyme that directly phosphorylates glucose in the liver, making it the correct answer.