Adenosine deaminase (ADA) is a purine catabolic enzyme ubiquitous in mammalian tissue which catalyzes deamination of both adenosine and 2'-deoxyadenosine to inosine and 2'-deoxyinosine respectively.
ADA is a class of nucleoside catabolic enzymes with significant links to the body's cellular immune system, comprising a group of thiol-containing hydrolases. ADA plays a pivotal role in purine nucleotide catabolism, catalysing the degradation of adenosine nucleosides into inosine nucleosides. These inosine nucleosides are subsequently phosphorylated by nucleoside phosphorylase into inosine, which is ultimately oxidised into the metabolic product uric acid.
ADA is widely distributed throughout the body, with the highest levels found in the thymus, spleen, and other lymphoid tissues. It is also present in the liver, kidneys, skeletal muscle, and lungs. In peripheral blood, lymphocytes and monocytes show the highest enzymatic activity. The activity in red blood cells and granulocytes is 40–70 times greater than that in serum, with T lymphocytes exhibiting higher activity than B lymphocytes.
Gel electrophoresis can distinguish between the ADA1, ADA2, and ADA2‑1 subtypes, whose phenotypes are controlled by the ADA1 and ADA2 alleles on chromosome 20. Typing can generally be performed using three-month-old blood spots. Among the Han Chinese population in China, ADA1 accounts for about 95% of cases, while among ethnic minorities it constitutes approximately 84%. The ability to distinguish individual ADA subtypes remains relatively limited.
