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AMP-activated protein kinase

Abbreviation: AMPK
German: AMP-abhängige Kinase

1 Definition

AMP-activated protein kinase, AMPK for short, is a kinase enzyme found in all eukaryotic cells. It is activated by adenosine monophosphate (AMP) and plays an important role in the regulation of enzymes in situations of a cellular lack of energy.

2 Biochemistry

Like many other enzymes, AMP-activated protein kinase exists in an inactive dephosphorylated form, and in an active phosphorylated form. When AMP binds to the inactive dephosphorylated form, the resulting complex can serve as a substrate for the constitutively active protein kinase AMP kinase (LKB1), which in turn activates AMPK by phosphorylating it. The inactivation of AMPK is carried out by a protein phosphatase. In addition, AMPK can be activated by other stimuli, e.g. hypoxia, many other stress responses, and also by the adiponectin protein, which is secreted by adipose tissue.

2.1 Effects of AMP-activated kinase

Activated AMPK can regulate other proteins by phosphorylating them. It inhibits, for instance, the key enzymes of the cholesterol and fatty acid biosynthesis, the HMG-CoA reductase or acetyl-CoA carboxylase. It furthermore inhibits glycogen synthesis. An example for an enzyme which is activated by AMPK is phosphofructokinase 2, the phosphorylation of which results in increased glycolysis. AMPK inhibits protein biosynthesis and consequently cell growth by inactivating mTOR. Further direct or indirect effects of AMPK include the activation of beta oxidation, the inhibition of protein biosynthesis, and the GLUT 4 translocation to the cell membrane. Overall, the activation of AMPK results in lowered AMP levels and corresponding increase of ATP levels.

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