Adenosine aminohydrolase from human spleen: partial purification and some kinetic properties

Adenosine aminohydrolase from human spleen was purified 120 fold. In pH 7.3 phosphate buffer at 37 degrees, this enzyme preparation deaminated adenosine and arabinosyladenine (ara-A) with apparent values for the Michaelis constant of 40 muM and 90 muM respectively. The products of both deamination reactions, i.e., inosine and arabinosylhypoxanthine, were competitive inhibitors with Ki equal to 710 muM and 60 muM, respectively. N6-benzyladenosine and 2'-deoxy-N6-benzyladenosine were competitive inhibitors. The former was better able to inhibit ara-A than adenosine deamination, while the latter was equivalent in inhibiting deamination of these two substrates. Evidence for a naturally occurring adenosine aminohydrolase inhibitor in spleen was presented. It is suggested that benzyladenosine and deoxybenzyladenosine might potentiate ara-A chemotherapy of neoplasms and metastates in the spleen and other hemic cells.