– Purine Nucleoside Phosphorylase, an essential enzyme in purine metabolism, plays a critical role in the purine salvage pathway. Its deficiency impairs T cell function. With inorganic orthophosphate as a co-substrate, this enzyme catalyzes the cleavage of the glycosidic bond linking ribose and deoxyribonucleoside, resulting in the production of a purine base and ribose (deoxyribose)-1-phosphate [1].