Regulation of Glycolysis

Regulatory mechanisms controlling glycolysis include allosteric and covalent modification mechanisms.

Glycolysis is regulated reciprocally from gluconeogenesis. Molecules, such as F2,6BP, that turn on glycolysis, turn off gluconeogenesis. Conversely, acetyl-CoA turns on gluconeogenesis, but turns off glycolysis. See Figure 16.6

The principle enzymes of glycolysis involved in regulation are hexokinase (reaction 1), phosphofructokinase (reaction 3), and pyruvate kinase (reaction 10):

> 1. Hexokinase is allosterically inhibited by glucose-6-phosphate (G6P). That is, the enzyme for the first reaction of glycolysis is inhibited by the product of the first reaction. As a result, glucose and ATP (in reactions 1 and 3) are not committed to glycolysis unless necessary.

> 2. Phosphofructokinase (PFK) is a major control point for glycolysis. PFK is allosterically inhibited by ATP and citrate, allosterically activated by AMP, ADP, and F2,6BP. Thus, carbon movement through glycolysis is inhibited at PFK when the cell contains ample stores of ATP and oxidizable substrates. Additionally, PFK is activated by AMP and ADP because they indicate low levels of ATP in the cell. F2,6BP is the major activator, though, because it reciprocally inhibits fructose 1,6 bisphosphatase, which is the gluconeogenic enzyme that catalyzes the reversal of this step.

> 3. Pyruvate kinase is allosterically inhibited by acetyl-CoA, ATP, and Alanine; allosterically activated by F1,6BP, and inhibited by cAMP-dependent phosphorylation.

Note that several of the allosteric regulators are products of other metabolic pathways or are made in other metabolic pathways. These include acetyl-CoA, AMP, F2,6BP, and G1P, (readily converted into G6P). By having regulation dependent on other pathways, glycolysis is coordinately controlled with these pathways as well.

See also: Gluconeogenesis and Glycolysis Interregulation Link Page, Hexokinase, G6P, AMP,