Metabolism — glycolysis (step 7)

Phosphoglycerate kinase: first ATP-generating step

How the Phosphoglycerate kinase works, in 3 steps. Each step shows the structures and the curved arrows that move the electrons.

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In short. A 3-step mechanism. Typical reagents: 1,3-Bisphosphoglycerate, ADP, Mg²⁺, phosphoglycerate kinase. Conditions: Cytosol, pH ≈ 7.4, 37 °C. Bonds formed: ATP (P–O bond); 3-phosphoglycerate carboxylate; bonds broken: Acyl–phosphate (C–O–P) anhydride. Stereochemistry: In-line SN2-like phosphoryl transfer at P. Rate and selectivity: Near equilibrium in cells; pulled forward by downstream steps.

At a glance

Reagents1,3-Bisphosphoglycerate, ADP, Mg²⁺, phosphoglycerate kinase

Solvent / conditionsCytosol, pH ≈ 7.4, 37 °C

Bonds formedATP (P–O bond); 3-phosphoglycerate carboxylate

Bonds brokenAcyl–phosphate (C–O–P) anhydride

StereochemistryIn-line SN2-like phosphoryl transfer at P

Rate / selectivityNear equilibrium in cells; pulled forward by downstream steps

Step 1: High-energy acyl phosphate and ADP

1,3-Bisphosphoglycerate carries a mixed carboxylic-phosphoric anhydride, an acyl phosphate whose phosphoryl-transfer potential is higher than ATP's. This is the high-energy bond created in the GAPDH step.

Step 2: In-line attack on phosphorus

The terminal oxygen of ADP attacks the acyl phosphate's phosphorus in-line, with Mg²⁺ helping hold the phosphates in place. The carboxylate oxygen is the leaving group, so the phosphoryl group is transferred without a covalent enzyme intermediate.

Step 3: ATP and 3-phosphoglycerate

The products are 3-phosphoglycerate and ATP. Because it makes ATP from a substrate (not from the electron transport chain), this is called substrate-level phosphorylation. It pays back the ATP invested at the hexokinase and PFK-1 steps.

Abbreviations and terms

SN2: Bimolecular nucleophilic substitution. One concerted step with backside attack and inversion; rate = k[RX][Nu].
ATP: Adenosine triphosphate. The cell’s energy currency; transfers phosphate groups.
ADP: Adenosine diphosphate. ATP after losing one phosphate.
GAPDH: Glyceraldehyde-3-phosphate dehydrogenase. Glycolytic enzyme oxidising G3P with NAD⁺.
PFK-1: Phosphofructokinase-1. The key regulated, committed step of glycolysis.

How it compares with related reactions

	Phosphoglycerate kinase	Enolase	GAPDH
Reagents	1,3-Bisphosphoglycerate, ADP, Mg²⁺, phosphoglycerate kinase	2-Phosphoglycerate, 2 Mg²⁺, enolase (Lys345 base, Glu211 acid)	Glyceraldehyde-3-phosphate (G3P), NAD⁺, inorganic phosphate (Pi), GAPDH (Cys149, His176)
Conditions	Cytosol, pH ≈ 7.4, 37 °C	Cytosol, pH ≈ 7, 37 °C	Aqueous, pH ≈ 7.4, 37 °C (cytosol)
Stereochemistry	In-line SN2-like phosphoryl transfer at P	Anti elimination of H and OH; reversible	Hydride delivered to one face of NAD⁺ (pro-R)
Rate / selectivity	Near equilibrium in cells; pulled forward by downstream steps	ΔG°′ ≈ +1.8 kJ/mol; PEP has a very high phosphoryl-transfer potential	Fast and reversible; couples oxidation to phosphate capture

Test yourself

Try to answer each question before opening it.

Which reagents and conditions are typical for the Phosphoglycerate kinase?

1,3-Bisphosphoglycerate, ADP, Mg²⁺, phosphoglycerate kinase. Conditions: Cytosol, pH ≈ 7.4, 37 °C.

Which bonds are formed and which are broken?

Formed: ATP (P–O bond); 3-phosphoglycerate carboxylate. Broken: Acyl–phosphate (C–O–P) anhydride.

What is the stereochemical outcome?

In-line SN2-like phosphoryl transfer at P

What controls the rate or the selectivity?

Near equilibrium in cells; pulled forward by downstream steps

Study guides that help with this reaction

Related mechanisms

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