Glükokiinasi

Glükokiinasi, also known as hexokinase IV, is an enzyme found primarily in the liver and pancreatic beta cells. It plays a crucial role in glucose metabolism by catalyzing the phosphorylation of glucose to glucose-6-phosphate. This reaction is the first step in both glycolysis and glycogen synthesis. Unlike other hexokinases, glükokiinasi has a high Km value for glucose, meaning it is only significantly active when glucose concentrations are elevated, such as after a meal. This characteristic allows it to act as a glucose sensor.

In the liver, glükokiinasi's activity regulates glucose uptake and storage as glycogen, helping to prevent hyperglycemia after eating. When blood glucose levels rise, glükokiinasi becomes more active, facilitating the conversion of glucose into glucose-6-phosphate, which can then be used for energy or stored. Conversely, when glucose levels fall, its activity decreases, slowing down glucose consumption and promoting glucose release from glycogen stores.

In pancreatic beta cells, glükokiinasi's function is essential for insulin secretion. When blood glucose rises, glükokiinasi phosphorylates glucose, leading to increased ATP production. This ATP then closes ATP-sensitive potassium channels, causing depolarization of the cell membrane and opening of voltage-gated calcium channels. The influx of calcium ions triggers the release of insulin. Mutations in the glükokiinasi gene can lead to diabetes mellitus, either by reducing insulin secretion or by affecting hepatic glucose regulation.