I.U.B.: 3.5.4.4
Adenosine aminohydrolase
Adenosine deaminase (ADA) is a purine catabolic enzyme ubiquitous in mammalian tissue. In vitro it catalyzes deamination of both adenosine and 2'-deoxyadenosine to inosine and 2'-deoxyinosine respectively.
Barankiewicz and Cohen (1984) report on catabolic pathways involving ADA.
Lack of erythrocyte ADA has been shown to be associated with inherited severe combined immunodeficiency (SCID), Hirschhorn et al. (1976), Trotta et al. (1976), Meuwissen et al. (1975), Meuwissen and Pollara (1974), Yount et al. (1974) and Ochs et al. (1973). Giblett et al. (1972) hypothesized that since RBC-ADA is similar to that produced by normal lymphocytes, its lack in inherited immune disease is due to impaired lymphocyte function. (SCID is characterized by deficiencies in both B and T cell-mediated immunity and with the onset, early in life, of severe infections). van de Weydan et al. (1974) report on the reductions of splenic ADA in SCID. Green and Chan (1973) suggest that the immune deficiency disease associated with lack of ADA may be the result of pyrimidine starvation. See also Delia et al. (1987).
Hirschhorn et al. (1980) report on the amelioration of neurologic abnormalities after "enzyme replacement" and Herschfield et al. (1987) report on treatment of ADA deficiency with polyethylene glycol-modified ADA. It is indicated that polyethylene glycol covalently attached to bovine ADA diminishes immunogenicity, inhibits attack by degradative enzymes, and prolongs plasma half-life. See also Davis et al. (1981).
Trams and Lauter (1975) conjecture that ADA has a role in modulating neuron membrane permeability and thus cellular excitability. Ressler (1969) indicated its primary function to be detoxification of pharmacologically active adenosine.
Several isozymes and inherited variants have been described (Spencer et al. 1968; Edwards et al. 1971). Hirschhorn (1975) indicates that tissue specific ADA isozymes may be generated from a single red blood cell-ADA molecule coded by a single genetic locus; thus, a deficiency in RBC-ADA would result in a deficiency in other tissue.
Akedo et al. (1972) report no significant enzymatic or immunological differences in the isozymes. Ressler (1969) also reported interconversions of different forms from a single primary molecule. It has been reported that the molecular weights reflected physiological and pathological states of the cells from which derived (Akedo et al. 1972). Nishihara et al. (1973) report on a factor that converts the small human ADA molecules (MW 47,000) into large molecules (MW 230,000). See also Agarwal et al. (1975).
Measurement of serum ADA shows elevation in primary liver disease and secondary hepatic neoplasia, and according to Ellis et al. (1973), it is the most useful single test in portal cirrhosis. Piras and Gakis (1973) report that cerebrospinal fluid ADA is elevated in tuberculous meningitis. Nishizawa et al. (1975) indicate elevated RBC-ADA in gouty subjects. See Norstrand (1987) re various neurological conditions, and Ribera et al. (1987) re tuberculous meningitis, Segura et al. re tuberculosis.
According to Coleman and Hutton (1975) there is considerable interest in monitoring ADA activity in patients with a variety of defects in cellular and humoral immunity. See also Korber et al. (1975). Tritsch and Mittelman (1975) report on an automated ADA method using continuous flow analysis.
Characteristics of Adenosine Deaminase from Calf Spleen
(Pfrogner 1967):
Molecular Weight: 32,500 - 33,000.
Composition: The enzyme is a glycoprotein containing galactosamine and glucosamine. Its composition shows a predominance of acidic amino acids.
Optimum pH: 6.3.
Isoelectric point: pH 4.85.
Activators: None reported; no metal ion requirements reported.
Specificity: Adenosine and deoxyadenosine were deaminated at about the same rate. This was also reported by O'Brien and Tully (1968). (Zemlicka 1975, has reported on ADA substrate conformations using calf-intestine enzyme).
Inhibitors: Ag+, Hg2+, Cu2+, sulfhydryl reagents (pCMB and methyl mercuric nitrate) are strongly inhibiting. The even stronger inhibiting effect of TPCK and DFP suggests that histidine or serine or both might play a role in the active site of the enzyme. See also Cristalli, et al. (1988).
Stability: The enzyme was found to be stable at pH 4-10 up to 65°C for 15 minutes. A solution of 1 unit per ml was maintained without loss of activity for 3 months at -50°C. The enzyme is stable for 6 - 9 months when stored at 2 - 8°C.
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