Glucose phosphorylation and dephosphorylation in chicken liver

Area of Science:

• Biochemistry
• Cellular Metabolism
• Avian Physiology

Background:

• Hexokinases are crucial enzymes in glucose metabolism, responsible for the initial phosphorylation of glucose.
• Glucose-6-phosphatase (G6Pase) plays a vital role in glucose homeostasis by dephosphorylating glucose-6-phosphate.
• Understanding the specific roles of these enzymes in avian liver metabolism is essential for comprehending glucose regulation in chickens.

Purpose of the Study:

• To investigate the presence and characteristics of glucokinase and hexokinases in chicken liver.
• To determine the kinetic properties of glucose-6-phosphatase in chicken liver under different nutritional states.
• To elucidate the regulatory roles of hexokinases and glucose-6-phosphatase in chicken hepatocyte glucose transport.

Main Methods:

• Enzyme activity assays were performed on chicken liver homogenates.
• Kinetic parameters (Km) for glucose-6-phosphatase were determined.
• The effects of starvation and oral glucose administration on enzyme activities were evaluated.

Main Results:

• Glucokinase was not detected in chicken liver; only low Km hexokinases were present, sensitive to AMP and ADP but not ATP.
• Starvation reduced hexokinase activity but increased glucose-6-phosphatase activity and lowered its Km for glucose-6-phosphate.
• Oral glucose administration rapidly normalized enzyme activities to fed levels.

Conclusions:

• Chicken liver glucose uptake and efflux are primarily regulated by glucose-6-phosphatase activity and kinetics, as well as glucose-6-phosphate concentration.
• Hexokinases appear to have a limited regulatory function in chicken hepatocyte glucose transport.
• The findings highlight the critical role of glucose-6-phosphatase in avian glucose metabolism.