Human Adenosine Deaminase: Stoichiometry of the Large form Complex
Adenosine deaminase (adenosine aminohydrolase, ADA, EC 18.104.22.168.) is widely distributed in human tissues. In some tissues ADA exists exclusively as the small molecular form (36,000–38,000) while in other tissues the large molecular form of the enzyme predominates (298,000).1 The small form of ADA has been purified to homogenity from human erythrocytes and was shown to be a single polypeptide of molecular weight 38,000.2,3 Physical and kinetic characteristics of small form ADA from various tissues appeared to be identical to the purified erythrocyte enzyme.1,2 The small form of the enzyme could be converted to the large form ADA by incubation with a specific ADA binding protein (BP) (also termed complexing protein or conversion factor).1,4,5 This purified binding protein from human kidney was shown to be a dimer of identical subunits with a native molecular weight of 190,000–200,000.4,5 The large form ADA produced in vitro was physically and kinetically indistinguishable from the native large form ADA from various tissues.1,4
KeywordsAdenosine Deaminase Large Form Small Form Radioactive Peak Native Molecular Weight
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