Which enzyme performs the first step of glycolysis?

The correct answer is hexokinase, as it catalyzes the first step of glycolysis by phosphorylating glucose to form glucose-6-phosphate. This reaction is essential because it effectively traps glucose within the cell (as glucose-6-phosphate cannot easily cross the cell membrane) and prepares it for further breakdown in the glycolytic pathway. Hexokinase has a high affinity for glucose, allowing it to function well in various cellular conditions, and it operates in numerous tissues, which is crucial for maintaining energy homeostasis.

While glucokinase also catalyzes the phosphorylation of glucose to glucose-6-phosphate, it primarily operates in the liver and pancreas and is regulated differently than hexokinase, making hexokinase the more general enzyme involved in the first step of glycolysis across a broader range of tissues. Lactate dehydrogenase and fructokinase, on the other hand, are not involved in the initial phase of glycolysis, with lactate dehydrogenase playing a role in anaerobic metabolism and fructokinase acting on fructose rather than glucose.