Purine Metabolism in Intact Cells from a Purine Nucleoside Phosphorylase Deficient Child
Deficiencies of two subsequent enzymes in the purine degradation pathway, Adenosine Deaminase (ADA) and Purine Nucleoside Phosphorylase (PNP), result in immunodeficiency in children (1–3). PNP deficient patients accumulate large amounts of all four PNP substrates, inosine, deoxyinosine, guanosine and deoxyguanosine in their plasma and urine (4,5). Moreover, the total urinary purine excretion by PNP deficient patients is several fold higher than the equivalent uric acid excretion by normal children (4,5). This observation indicates that the purine salvage pathway in humans is remarkably active and that PNP does not serve merely as a degrading enzyme, but it may also play a role in the reutilization of purines. The tissue(s) responsible for reutilization of purine has not been identified. It has been suggested that purine reutilization represents a means by which purines are transported from the liver a tissue with active purine de novo biosynthesis, to be reutilized by peripheral tissue(s). Alternatively, it may be that purine reutilization is mainly an intracellular process since most tissues have both purine de novo and purine salvage pathways.
KeywordsAdenosine Deaminase Purine Metabolism Purine Nucleoside Phosphorylase Total Incorporation Subsequent Enzyme
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