Ectonucleotidases consist of families of

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

that are expressed on the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

and have externally oriented active sites. These enzymes metabolize

s to nucleosides. The contribution of ectonucleotidases in the modulation of

purinergic signaling Purinergic signalling (or signaling: see American and British English differences) is a form of extracellular signalling mediated by purine nucleotides and nucleosides such as adenosine and ATP. It involves the activation of purinergic receptor ...

depends on the availability and preference of substrates and on cell and tissue distribution.

Classification

Subfamilies of ectonucleotidases include:

CD39 Ectonucleoside triphosphate diphosphohydrolase-1 (gene: ''ENTPD1''; protein: NTPDase1) also known as CD39 (Cluster of Differentiation 39), is a typical cell surface enzyme with a catalytic site on the extracellular face. Function NTPDase1 is an ...

/NTPDases (ecto-nucleotide triphosphate diphosphohydrolases), Nucleotide pyrophosphatase/phosphodiesterase (NPP)-type ecto-phosphodiesterases, alkaline phosphatases and ecto-5’-nucleotidases/ CD73.

Function

Ectonucleotidases produce key molecules for purine salvage and consequent replenishment of ATP stores within multiple cell types. Dephosphorylated nucleoside derivatives interact with membrane transporters to enable intracellular uptake. Ectonucleotidases modulate P2 purinergic signaling, and

P1 receptors The adenosine receptors (or P1 receptors) are a class of purinergic G protein-coupled receptors with adenosine as the endogenous ligand. There are four known types of adenosine receptors in humans: A1, A2A, A2B and A3; each is encoded by a di ...

. In addition, ectonucleotidases generate extracellular adenosine, which abrogates nucleotide-mediated effects and activates adenosine receptors, often with opposing (patho-) physiological effects.

Adenosine generation

The first step in the production of adenosine involves the conversion of ATP/ADP to AMP. It is carried out by ENTPD1, also known as CD39. The second step involves the conversion of AMP to adenosine. It is carried out by

NT5E 5′-nucleotidase (5′-NT), also known as ecto-5′-nucleotidase or CD73 (cluster of differentiation 73), is an enzyme that in humans is encoded by the ''NT5E'' gene. CD73 commonly serves to convert AMP to adenosine. Transcription factor bindin ...

, also known as CD73.

References

Hydrolases Purinergic signalling {{Enzyme-stub