Which enzyme is responsible for phosphorylating glucose in the first step of glycolysis?

The enzyme that phosphorylates glucose in the first step of glycolysis is hexokinase. This reaction is essential as it converts glucose into glucose-6-phosphate, which is a key step in the metabolic pathway. This phosphorylation traps glucose inside the cell and prepares it for further breakdown, allowing the cell to utilize glucose as an energy source.

Hexokinase phosphorylates glucose using the energy from ATP, highlighting the enzyme's role in the regulation of glucose metabolism. Although glucokinase also phosphorylates glucose, it is primarily found in the liver and has a different regulatory mechanism than hexokinase, which is present in most tissues and operates efficiently even at low glucose concentrations. This distinction is important for understanding how different tissues manage glucose levels.

ATPase does not phosphorylate glucose; instead, it is involved in hydrolyzing ATP to release energy. Pyruvate kinase, on the other hand, participates in the later stages of glycolysis, specifically catalyzing the conversion of phosphoenolpyruvate to pyruvate, which occurs after the initial step involving glucose phosphorylation. Thus, hexokinase is the definitive enzyme responsible for the phosphorylation of glucose at the beginning of glycolysis.