Inhibition studies on membrane adenosine deaminase from human placenta.

The ecto form of adenosine deaminase isolated from human placental membrane was tested towards its sensitivity against adenosine deaminase inhibitors, such as aza and deaza analogues of adenosine and erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA). Ki values of the inhibitors observed were similar to these obtained for the small form of adenosine deaminase purified from human erythrocytes, indicating that the presence of the binding protein on placental adenosine deaminase does not produce alteration in the binding of these inhibitors on the enzyme active site. The inhibition rate of 2'-deoxycoformycin, one of the most potent ADA inhibitors is affected by the presence of the binding protein on human placental adenosine deaminase, that probably modulates the rearrangement of the active site produced by the binding with this tight-binding inhibitor.