Adenosine diphosphate

Adenosine diphosphate (ADP) is a nucleotide consisting of the diphosphate of the nucleoside adenosine. It is formed during the hydrolysis of adenosine triphosphate (ATP).

Adenosine with a one-part phosphorus chain is called adenosine monophosphate (AMP); with a three-part phosphorus chain it is called adenosine triphosphate (ATP). Of these three molecules, ATP is the most energy-rich molecule - AMP the least energy-rich.

The term high-energy or low-energy is actually misleading. The bonds are by no means strong, but rather unstable. Since all three phosphate groups in biological systems are negatively charged and are closely packed together, they repel each other; comparable to a taut spring. The divalent magnesium ion, coordinated under physiological conditions, stabilizes this tension somewhat.

Phosphorylation of substrates by ATP produces ADP, which can be generally formulated as follows:

{\displaystyle \mathrm {ATP+Substrat{\xrightarrow {Enzym}}Produkt+ADP} }

In this process, the bond between the second and third phosphate of the phosphate chain is broken and the substrate is phosphorylated. The product is more energy-rich than the substrate. The energy-poor ADP is phosphorylated again to the energy-rich ATP by energy-producing reactions in the body. In all eukaryotes, these reactions take place in the mitochondria, a special organelle of the cell. In plants that carry out photosynthesis, these build-up and breakdown reactions also take place in the chloroplasts.

Adenosine diphosphate also plays a role in platelet activation and thus platelet aggregation. ADP is released from dense granules in platelets and then interacts with a family of receptors on platelets (P2Y1, P2Y12, and P2X1).

See also

  • Adenylate kinase
  • ATP synthase

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