SECONDARY LOSS OF DEOXYGUANOSINE KINASE-ACTIVITY IN PURINE NUCLEOSIDEPHOSPHORYLASE DEFICIENT MICE

The T-cell immunodeficiency associated with purine nucleoside phosphor ylase (PNP) deficiency in man is believed to be due to the accumulatio n of dGTP which may be preferentially formed from deoxyguanosine in T- lymphocytes or their precursor cells. We found no evidence for dGTP ac cumulation in thymocytes or spleen leucocytes, < 1 nmol/10(9) cells, n or in erythrocytes, < 0.05 nmol/10(9) cells, of the B6-NPE- or B6-NPF PNP-deficient mice strains. There were no changes in purine or pyrimid ine ribonucleotide pools. As these mice had been previously shown to e xcrete PNP nucleoside substrates, we examined the metabolism of deoxyg uanosine. Deoxyguanosine kinase activity as compared to control mice w as 6 to 52% for the B6-NPE mutant, 2 to 22% for the B6-NPF mutant. Fra ctionation of erythrocyte and liver lysates from the F mutation and th e background strain, C57BL/6J, by anion exchange chromatography confir med the secondary deficiency of deoxyguanosine kinase and demonstrated that this activity was distinct from adenosine kinase and two major p eaks of deoxycytidine kinase activity. Mouse PNP, expressed and purifi ed as a fusion protein, did not show evidence of being bifunctional an d having deoxyguanosine kinase activity. Metabolic modelling revealed that the ratio of deoxyguanosine phosphorylation versus phosphorolysis was < 0.06 in control mice, and less than or equal to 0.3 in lymphocy tes of PNP-deficient mice. Were deoxyguanosine kinase not reduced in t he PNP-deficient mice, all tissues of the B6-NPF mutant would preferen tially phosphorylate deoxyguanosine at low substrate concentrations.