Purine nucleoside phosphorylase metabolic functions

K.C.Rich,E.Mejians,I.H.Fox. Purine nucleoside phosphorylase deficiency improved metabolic and immunological function with erythrocyte transfusion. N.Eng.J.Med.303 973 (1980). 

Adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiency have been recognized as the primary cause of an associated immune deficiency syndrome. A number of mechanisms have been proposed to explain the predominant effect of these enzyme deficiencies on the development and function of the lymphoid system. One of the mechanisms concerns the phosphorylation of accumulated metabolic compounds i.e. deoxyadenosine (dAdo) in case of ADA-deficiency and deoxyguanosine (dGuo) in case of PNP deficiency in the lymphoid cells and particularly in thymocytes (1). Indeed increased deoxyATP and deoxyGTP levels have been found in the lymphocytes of ADA- and PNP-deficient patients respectively (2,3). These triphosphates may inhibit the enzyme ribonucleotide reductase which leads to a depletion of deoxyCTP and interference with lymphocytic DNA-synthesis (1). 

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