In vivo inactivation of erythrocyte S-adenosylhomocysteine hydrolase by 2'-deoxyadenosine in adenosine deaminase-deficient patients

The cytotoxic nucleoside 2'-deoxyadenosine is excreted in excessive amounts by individuals with genetic deficiency of adenosine deaminase, and may be in part responsible for the severe combined immune dysfunction from which they suffer. Earlier studies from this laboratory showed that 2'-deoxyadenosine causes the irreversible inactivation of the enzyme S-adenosylhomocysteine hydrolase by an active site-directed, 'suicide-like' process. In this communication the authors have demonstrated similar inactivation of S-adenosylhomocysteine hydrolase in hemolysate and in intact erythrocytes, as well as a striking deficiency of S-adenosylhomocysteine hydrolase activity in the erythrocytes of 3 adenosine deaminase-deficient patients. In vivo suicide-like inactivation of S-adenosylhomocysteine hydrolase by 2'-deoxyadenosine may contribute to the cytotoxicity of 2'-deoxyadenosine and to the immune dysfunction in adenosine deaminase deficiency.