hexokinaseglukokinase

Hexokinase and Glucokinase are enzymes that catalyze the first step in glycolysis, the phosphorylation of glucose. Hexokinase is a ubiquitous enzyme found in most tissues, while glucokinase is primarily found in the liver and pancreatic beta cells. Both enzymes convert glucose into glucose-6-phosphate, a crucial intermediate in glucose metabolism. The key difference lies in their kinetic properties and regulatory mechanisms.

Hexokinase has a low Km and is saturated with glucose at physiological concentrations. This means it functions efficiently even at low blood glucose levels, ensuring that glucose is taken up and phosphorylated by most tissues for energy production. Hexokinase is also subject to product inhibition by glucose-6-phosphate, preventing excessive glucose phosphorylation.

Glucokinase, on the other hand, has a high Km and is not saturated with glucose at typical blood glucose levels. This means its activity is highly dependent on glucose concentration. In the liver, glucokinase's high Km allows it to respond to fluctuations in blood glucose. When blood glucose is high, such as after a meal, glucokinase efficiently phosphorylates glucose, promoting its storage as glycogen or conversion to fatty acids. When blood glucose is low, glucokinase activity decreases, allowing glucose to be released into circulation. In pancreatic beta cells, glucokinase acts as a glucose sensor. Its activity determines the rate of glucose-induced insulin secretion.