# AMP-activated protein kinase
**AMP-activated protein kinase** (AMPK) is a heterotrimeric serine/threonine kinase found in almost all eukaryotes that senses cellular energy status and maintains energy homeostasis by switching on ATP-generating catabolic pathways and switching off ATP-consuming anabolic ones.[1](https://onlinelibrary.wiley.com/doi/10.1111/cbdd.12897) • [2](https://pubmed.ncbi.nlm.nih.gov/21325438/) It is widely studied as a drug target for type 2 diabetes, metabolic diseases, cancers, and cardiovascular disease.[1](https://onlinelibrary.wiley.com/doi/10.1111/cbdd.12897)
| Key fact | Detail |
|---|---|
| Structure | Heterotrimer of a catalytic α subunit and regulatory β and γ subunits in a 1:1:1 complex; mammalian isoforms α1/α2, β1/β2, γ1/γ2/γ3[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) |
| Primary activation switch | Phosphorylation of Thr172 in the activation loop of the α subunit, which increases activity up to ~100-fold in vitro[4](https://doi.org/10.1016/j.molcel.2017.05.032) |
| Allosteric signal | AMP binding to the γ subunit; combined AMP and phosphorylation produces a >1000-fold activity increase, whereas AMP alone elicits only about a 5-fold maximum increase[5](https://www.ahajournals.org/doi/pdf/10.1161/circep.112.972265) |
| Energy signal sensed | The AMP:ATP ratio, which varies approximately as the square of the ADP:ATP ratio because adenylate kinase (2ADP ↔ ATP + AMP) operates near equilibrium[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC2867412/) |
| Downstream targets | More than 100 identified; acetyl-CoA carboxylase (ACC) was the first[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) |
| Evolutionary origin | The α subunit is the mammalian orthologue of Snf1, the catalytic subunit of the yeast glucose-starvation kinase[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) |
| Key activators | Indirect: metformin, exercise, glucose deprivation; direct: AICAR (via ZMP), A-769662, salicylate, MK-8722[7](https://www.nature.com/articles/emm201616) |
## Structure and isoforms
AMPK is an αβγ heterotrimer. The α subunit carries the catalytic kinase domain, while the β and γ subunits are regulatory.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC4834453/) Complete purification in 1994 by [D. Grahame Hardie](https://www.edgepedia.org/d-grahame-hardie)'s group at the University of Dundee and Bruce Kemp's group in Melbourne revealed the three subunits, and subsequent cloning identified two α isoforms, two β isoforms, and three γ isoforms in mammals.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) The γ subunit contains the allosteric [AMP-binding](https://www.edgepedia.org/amp-binding) site, first demonstrated with a reactive AMP analog.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/)
Different heterotrimer combinations respond differently to physiological signals. In human skeletal muscle, γ3-containing complexes are predominantly activated by exercise, while α2β2γ1 and α1β2γ1 heterotrimers are unchanged or activated only after prolonged exercise.[9](https://www.ncbi.nlm.nih.gov/books/NBK543786/)
## Activation mechanism
AMPK activation occurs by a dual mechanism involving allosteric activation and phosphorylation by upstream kinases.[2](https://pubmed.ncbi.nlm.nih.gov/21325438/) The phosphorylation step targets a conserved threonine in the activation loop of the α subunit, Thr174 in α1 and Thr172 in α2, conventionally called Thr172.[9](https://www.ncbi.nlm.nih.gov/books/NBK543786/) Phosphorylation at this site is essential for activation and increases activity by roughly 100-fold.[4](https://doi.org/10.1016/j.molcel.2017.05.032) • [6](https://pmc.ncbi.nlm.nih.gov/articles/PMC2867412/)
**Three effects of AMP.** Binding of AMP to the γ subunit does more than activate the enzyme allosterically, a moderate 2- to 10-fold effect. It also increases the susceptibility of the α subunit to phosphorylation at Thr172 by upstream kinases and decreases its accessibility to protein phosphatases.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC4834453/) Early evidence for this came from experiments in which rat hepatocytes treated with 20 mM fructose showed a transient 10-fold fall in ATP mirrored by a greater than 100-fold rise in AMP, accompanied by transient AMPK activation that persisted even when allosteric effects were lost during assay, indicating a covalent change.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) Later work showed directly that AMP binding inhibits Thr172 dephosphorylation.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) In heart preparations, combined activation by AMP and phosphorylation produces a greater than 1000-fold increase in activity, against about 5-fold for AMP alone.[5](https://www.ahajournals.org/doi/pdf/10.1161/circep.112.972265)
**Why AMP is the signal.** The main source of cellular AMP is the adenylate kinase reaction, 2ADP ↔ ATP + AMP, which runs close to equilibrium in most cells. Under this condition the AMP:ATP ratio varies as the square of the ADP:ATP ratio, making AMP a much more sensitive indicator of falling energy status than ADP itself.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) • [6](https://pmc.ncbi.nlm.nih.gov/articles/PMC2867412/) Increases in AMP in stressed cells are therefore always much larger than increases in ADP or decreases in ATP.[10](https://www.sciencedirect.com/science/article/abs/pii/S0955067414001069)
## Upstream kinases
The upstream kinase that phosphorylates Thr172 was purified from rat liver in the 1990s and shown to target Thr172 on the α subunit.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) Two major upstream kinases in the heart are liver kinase B1 (LKB1, also known as serine/threonine kinase 11) and Ca2+/calmodulin-dependent protein kinase kinase (CaMKK).[5](https://www.ahajournals.org/doi/pdf/10.1161/circep.112.972265) Transforming growth factor-β activated kinase 1 (TAK1) also phosphorylates AMPK at Thr172 in response to TGF-β, bone morphogenic protein, or Wnt signaling.[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC4834453/)
## Discovery history
The kinase activity was first described in 1973, when David Gibson's group in [Indianapolis](https://www.edgepedia.org/indianapolis) detected a putative kinase in crude rat liver extract that phosphorylated and inactivated [HMG-CoA reductase](https://www.edgepedia.org/hmg-coa-reductase), and Ki-han Kim's group independently showed ATP-dependent inactivation of acetyl-CoA carboxylase.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) • [11](https://theses.gla.ac.uk/83971/1/2023HwejPhD.pdf) In the 1980s, Hardie's laboratory in Dundee purified what they called ACC kinase-3 (ACK3) and showed that after 700- to 1000-fold purification from rat liver it inactivated both ACC and HMG-CoA reductase, with both activities allosterically activated by AMP, establishing that the two activities belonged to one enzyme.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) As further targets accumulated, the enzyme was renamed AMP-activated protein kinase after its allosteric activator, with the name first used in 1988.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/) Annual PubMed mentions of AMPK passed 10 in 1992, 100 in 2002, and 1000 in 2011.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/)
## Physiological roles
AMPK is activated by conditions that deplete cellular energy, including nutrient starvation (especially glucose deprivation), hypoxia, ischemia, exercise, and toxins that inhibit the mitochondrial respiratory chain.[7](https://www.nature.com/articles/emm201616) • [12](https://www.ncbi.nlm.nih.gov/books/NBK543781/pdf/Bookshelf_NBK543781.pdf) Once active, it promotes glucose transport and fatty acid oxidation while suppressing glycogen synthase activity and protein synthesis.[13](https://arxiv.org/abs/1911.02345) In metabolic terms it switches off ATP-consuming pathways such as fatty acid and cholesterol synthesis and switches on ATP-generating processes such as glucose uptake and fatty acid oxidation.[14](https://www.e-dmj.org/upload/pdf/dmj-37-1.pdf)
Beyond metabolism, AMPK participates in regulating the cell cycle, cell polarity, autophagy, and life span.[1](https://onlinelibrary.wiley.com/doi/10.1111/cbdd.12897) Its effects extend into cardiac electrophysiology, where a role in arrhythmia generation has been proposed.[5](https://www.ahajournals.org/doi/pdf/10.1161/circep.112.972265)
## Pharmacological activators
**Indirect activators** raise cellular AMP:ATP ratios. Metformin, a first-line antidiabetic drug, inhibits complex I of the mitochondrial respiratory chain, increasing the AMP:ATP ratio; it fails to activate AMPK in cells expressing the AMP-insensitive R531G AMPKγ2 subunit, supporting this indirect mechanism.[7](https://www.nature.com/articles/emm201616) Other indirect activators include 2-deoxyglucose, which inhibits glycolysis, and dinitrophenol, which uncouples mitochondria.[15](https://ojs.srce.hr/periodicum_biologorum/article/download/10802/8483)
**Direct activators** bind the AMPK complex. AICAR, the first direct activator, is an adenosine analog taken up by cells and phosphorylated by adenosine kinase to the AMP-mimetic ZMP, which binds the γ subunit in place of AMP.[7](https://www.nature.com/articles/emm201616) • [16](https://pubmed.ncbi.nlm.nih.gov/25241895/) A-769662 and salicylate bind the ADaM (allosteric drug and metabolite) site, as does MK-8722, which activates all 12 mammalian AMPK complexes and induces robust, durable, insulin-independent glucose uptake and glycogen synthesis in skeletal muscle.[15](https://ojs.srce.hr/periodicum_biologorum/article/download/10802/8483) • [17](https://pmc.ncbi.nlm.nih.gov/articles/PMC9312068/)
**Caveats for research use.** Comparisons of six common AMPK agonists (metformin, [phenformin](https://www.edgepedia.org/phenformin), AICAR, 2-deoxy-D-glucose, salicylate, and A-769662) found that most display AMPK-independent effects on cell proliferation and metabolism, with only A-769662 exerting AMPK-dependent effects on these processes.[16](https://pubmed.ncbi.nlm.nih.gov/25241895/) AICAR likewise has documented AMPK-independent effects in liver and adipose tissue.[18](https://journals.physiology.org/doi/full/10.1152/ajpendo.00225.2016) Whether direct AMPK activation is beneficial and safe over the long term remains to be established for specific diseases.[19](https://pubmed.ncbi.nlm.nih.gov/30867601/)
## References
1. [Li, J., Li, S., Wang, F. and Xin, F. (2017). Structural and biochemical insights into the allosteric activation mechanism of AMP-activated protein kinase. Chem Biol Drug Des, 89: 663-669.](https://onlinelibrary.wiley.com/doi/10.1111/cbdd.12897)
2. [Hardie, D.G. (2011). Sensing of energy and nutrients by AMP-activated protein kinase. (PubMed review abstract)](https://pubmed.ncbi.nlm.nih.gov/21325438/)
3. [Hardie, D.G. (2022). AMP-activated protein kinase — a journey from 1 to 100 downstream targets. Biochem J 479(22):2327-2343.](https://pmc.ncbi.nlm.nih.gov/articles/PMC9704532/)
4. [AMPK: Mechanisms of Cellular Energy Sensing and Restoration of Metabolic Balance. Molecular Cell (2017).](https://doi.org/10.1016/j.molcel.2017.05.032)
5. [AMP-Activated Protein Kinase. Circulation: Arrhythmia and Electrophysiology (2012).](https://www.ahajournals.org/doi/pdf/10.1161/circep.112.972265)
6. [Role of the energy sensor AMP-activated protein kinase in renal physiology and disease. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC2867412/)
7. [AMPK activators: mechanisms of action and physiological activities. Experimental & Molecular Medicine (2016).](https://www.nature.com/articles/emm201616)
8. [Unraveling the Actions of AMP-activated Protein Kinase in Metabolic Diseases: Systemic to Molecular Insights. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC4834453/)
9. [The Energy Sensor AMPK: Adaptations to Exercise, Nutritional and Hormonal Signals. NCBI Bookshelf.](https://www.ncbi.nlm.nih.gov/books/NBK543786/)
10. [AMPK: positive and negative regulation, and its role in whole-body energy homeostasis. ScienceDirect.](https://www.sciencedirect.com/science/article/abs/pii/S0955067414001069)
11. [PhD thesis, University of Glasgow (2023), section on AMPK history.](https://theses.gla.ac.uk/83971/1/2023HwejPhD.pdf)
12. [The Energy Sensor AMPK: Adaptations to Exercise, Nutritional and Hormonal Signals (PDF). NCBI Bookshelf.](https://www.ncbi.nlm.nih.gov/books/NBK543781/pdf/Bookshelf_NBK543781.pdf)
13. [The Energy Sensor AMPK: Adaptations to Exercise, Nutritional and Hormonal Signals (arXiv preprint).](https://arxiv.org/abs/1911.02345)
14. [Diabetes & Metabolism Journal (2013), AMPK-deficient mouse models review.](https://www.e-dmj.org/upload/pdf/dmj-37-1.pdf)
15. [Periodicum Biologorum, table of AMPK pharmacological activators and sites of action.](https://ojs.srce.hr/periodicum_biologorum/article/download/10802/8483)
16. [Differential effects of AMPK agonists on cell growth and metabolism. PubMed (2014).](https://pubmed.ncbi.nlm.nih.gov/25241895/)
17. [AMPK and Diseases: State of the Art Regulation by AMPK-Targeting Molecules. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC9312068/)
18. [Treatment of nonalcoholic fatty liver disease: role of AMPK. Am J Physiol-Endocrinol Metab.](https://journals.physiology.org/doi/full/10.1152/ajpendo.00225.2016)
19. [AMP-activated protein kinase: the current landscape for drug development. PubMed (2019).](https://pubmed.ncbi.nlm.nih.gov/30867601/)
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*Topic: Encyclopedia › Life and health › Biological foundations › Biochemistry and metabolism › Protein families and complexes › Kinase and phosphatase families › Protein kinase families*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license