Glyconeogenesis

Glyconeogenesis is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms.

Overview

Glyconeogenesis is a reverse process of glycolysis. It takes place in the cytoplasm and the mitochondria. The process uses several of the same enzymes and chemical reactions as glycolysis, but it has unique steps and enzymes as well.

Process

The process of glyconeogenesis starts with pyruvate, a product of glycolysis. Pyruvate is converted into phosphoenolpyruvate (PEP) by the enzyme pyruvate carboxylase and PEP carboxykinase. This is one of the unique steps in glyconeogenesis that is not simply a reversal of glycolysis.

The PEP is then converted back into glucose through a series of reactions that are mostly the reverse of glycolysis. However, there are three steps in glycolysis that are energetically irreversible and must be bypassed by four unique reactions in glyconeogenesis.

Regulation

Glyconeogenesis is tightly regulated at both the transcriptional and post-translational levels. This ensures that it only occurs when there is a need for glucose and not when glucose levels are high. The key regulatory points are the enzymes pyruvate carboxylase, fructose 1,6-bisphosphatase, and glucose 6-phosphatase.

Clinical significance

Defects in glyconeogenesis can lead to a variety of metabolic diseases, including hypoglycemia, lactic acidosis, and glycogen storage disease. Understanding the process of glyconeogenesis and its regulation can therefore be important in the diagnosis and treatment of these conditions.

See also

• Glycolysis
• Glucose metabolism
• Metabolic pathway