Purine nucleoside phosphorylase substrate specificity

The purine nucleoside phosphorylase activity of animal tissues cleaves both ribo- and deoxyribonucleosides of 6-oxypurines. For example, the the purine nucleoside phosphorylase of human erythrocytes has been highly purified and crystallized by Parks and co-workers 2) this enzyme will cleave the ribo- and deoxyribonucleosides of guanine and hypoxan-thine. Zimmerman et al. (3) have shown that purine nucleoside phosphorylase of several animal tissues has a low intrinsic activity toward adenine in the presence of ribose 1-phosphate. The cleavage of deoxyadenosine by highly purified preparations of the animal enzyme has not been reported but by analogy with adenosine, one might expect it also to be a poor substrate. The specificities of the purine nucleoside phosphorylases of E. coli and S. typhimurium differ from that of the animal enzyme in that adenosine and deoxyadenosine are readily phosphorolyzed H-6). 

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