Abstract
5'-Nucleotidase (5'-NT) has been reported to have an important role for the dephosphorylation of purine deoxynucleoside monophosphate. However, recent works have claimed that there is no evidence of a systemic reduction in the degradation of nucleotides in patients with 5'-NT deficiency. We re-evaluated a role of 5'-NT in normal human lymphocytes and obtained a possible result that acid phosphatase might be involved in the dephosphorylation of purine deoxyribonucleoside monophosphate rather than 5'-NT. Although adenine, which accumulates in adenine phosphoribosyl transferase (APRT) deficient patients, is cytotoxic to human lymphocytes in vitro, APRT deflations is not associated with immunodeficiency. Three possible solutions were tested for the normal immunity in APRT deficiency. One is that only the lymphocytes from APRT deficiency retain the APRT activity. The residual activity prevents lymphocytes from the accumulation of adenine. Another exists that adenine toxicity is dependent on the phosphorylation by APRT. The phosphorylated adenine disturbs the lymphocyte metabolism but not adenine itself. The last is that the oxidization of adenine to 2,8-dihydroxyadenine by xanthine oxidase is the protective mechanism by which the adverse effect of adenine is cancelled. However, none of these possibilities could account for the normal immunity in APRT deficiency. The precise mechanism remains to be elucidated.
