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Adenosine deaminase

Synonym: adenosine aminohydrolase
German: Adenosin-Desaminase

1 Definition

Adenosine deaminase (ADA) is an enzyme that catalyzes the transformation of adenosine to inosine and of deoxyadenosine to deoxyinosine.

2 Biochemistry

Adenosine deaminase occurs as a monomer and as a dimer. The monomeric form is a polypeptide chain which is folded in eight parallel alpha,beta-barrel domains. They form a central pouch which contains the active site of the enzyme. In addition to the 8 alpha helices and 8 beta sheets, ADA contains 5 more helices.

The active site contains a twice positively charged zinc ion which is fivefold coordinated by the amino acid positions His15, His17, His214, and Asp295, as well as the substrate.

2.1 Isoforms

Adenosine deaminase occurs in two isoforms:

3 Function

Adenosine deaminase plays an important role in the recycling process of purine nucleotides in mammals.

4 Clinical relevance

The hereditary adenosine deaminase deficiency leads to an accumulation of deoxyadenosine which is increasingly phosphorylated to dATP. The increased concentration of dATP inhibits the enzyme ribonucleotide reductase which in turn cuts off the synthesis of dADP, dGDP, dUDP, and dCDP. This results in a global interruption of DNA synthesis which mainly limits the proliferation of lymphocytes. This way an ADA deficiency can cause a severe combined immunodeficiency (SCID).

5 Pharmacology

The pharmacological effect of Cladribine relies on the inhibition of adenosine deaminase.

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