ATP is the energy store in all living cells
ATP is the intracellular "energy rich bonds" store.
Inside the cell ATP exists as a Mg salt; any molecule binds 2 Mg++ions, and most of intracellular Mg is in this form.
When ATP is bound to enzymes one Mg++ can be replaced by bonds with positively charged aminoacids (lysine and arginine)
When ATP is hydrolyzed to ADP and inorganic phosphate one Mg++ is lost
The intracellular ATP concentration is in the millimolar range, with large difference between tissues (5-20 mM):
- anaerobic (2 ATP/glucose)
- aerobic (38 ATP/glucose; 60? ATP/stearic acid)
Animation ATP synthase
- Intracellular ATPases
- Biosynthetic pathways
- Ionic gradients creation
a deeper insight
It has been known for almost 50 years that many cells carry enzymes that hydrolyze extracellular ATP, and the term "ecto-ATPase" was used first by Engelhardt 40 years ago. But until the end of the 1970's, the idea of an ATPase with its ATP hydrolyzing site on the outside of the cell membrane was met with substantial skepticism since it was thought that ATP was strictly intracellular. Nevertheless, ecto-ATPase activity was demonstrated using a variety of intact cells. Most ecto-ATPase(s) exhibited three common characteristics: 1) activation by either Ca2+ or Mg2+, 2) insensitivity to the commonly used inhibitors of F-type, P-type, and V-type ATPases, and 3) ability to hydrolyze nucleoside triphosphates and often nucleoside diphosphates as well. At the same time, the dominant ATPase activity in many plasma membrane preparations was shown to be distinct from the ion-pump ATPases, but had similar enzymatic properties as the ecto-ATPase(s). Thus the term "E-type ATPase activity" has been proposed for ATPase activity exhibiting these characteristics, and it is assumed that all ecto-ATPases are E-type ATPases.
The converse is not true, however, since soluble E-type ATPases were shown to exsist in plants, microorganisms, and the saliva of blood sucking insects. These enzymes could be easily purified, and exhibited very high specific activity. In contrast, the membrane bound E-type ATPases (the ecto-ATPases) were extremly difficult to isolate, and studies on partially purified preparations yielded conflicting and often controversial results with respect to enzymology and molecular identity.
Major histocompatibility class II transactivator (CIITA) expression in smooth muscle cells from A2b adenosine receptor knockout mice: crosstalk between the adenosine and IFN-gamma signaling.2008
AMPK is a serine/threonine protein kinase, which serves as an energy sensor in all eukaryotic cell types. (It is activated by high AMP/ATP ratio)
Energetics of Metabolism