- glucose --> glucose 6-phosphate by hexokinase G = -8.0 kcal/mole
Hexokinase also works on mannose and fructose at increased.
Serves to trap glucose in the cell --> a phosphorylated molecule cannot leave
- Glucose 6-phosphate --> fructose 6-phosphate by glucose 6-phosphate isomerase
Example of aldose--> ketose isomerization.
Enzyme is very stereospecific.
Reaction is near equilibrium in cell --> not a control point in glycolysis
- Fructose 6-phosphate --> fructose 1,6-bisphosphate by phosphofructokinase-1 (PFK-1)
Reaction has G = -5.3 kcal/mole and is metabolically irreversible.
Represents the first committed step in glycolysis.
- Fructose 1,6-bisphosphate --> dihydroxyacetone phosphate + glyceraldehyde 3-phosphate by fructose 1,6 bisphosphate aldolase.
- DHAP --> glyceraldehyde 3-phosphate by triose phosphate isomerase
Also catalyzes aldose--> ketose conversion.
Rate is diffusion controlled (substrate is converted to product as fast as substrate is encountered).
- glyceraldehyde 3-phosphate --> 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase
One molecule of NAD+ is reduced to NADH --> respiratory chain
- 1,3 bisphosphoglycerate --> 3-phosphoglycerate
Phosphoryl group transfer to ADP to form ATP.
Because phosphate group comes from a substrate molecule, called substrate level phosphorylation
First ATP-generating step of glycolysis.
- 3-phosphoglycerate --> 2-phosphoglycerate by phosphoglycerate mutase
Mutases are enzymes that transfer phosphoryl groups from one part of a substrate molecule to another.
2-phosphoglycerate --> phosphoenolpyruvate (PEP) by enolase (forms double bond)
- PEP --> pyruvate
Second time for substrate level phosphorylation.
Reaction is metabolically irreversible.(Figure)