Two fluorogenic substrates for purine nucleoside phosphorylase, selective for mammalian and bacterial forms of the enzyme.

Two nontypical nucleosides, 7-β-d-ribosyl-2,6-diamino-8-azapurine and 8-β-d-ribosyl-2,6-diamino-8-azapurine, have been found to exhibit moderately good, and selective, substrate properties toward calf and bacterial (Escherichia coli) forms of purine nucleoside phosphorylase (PNP). The former compound is effectively phosphorolysed by calf PNP and the latter by PNP from E. coli. Both compounds are fluorescent with λmax∼425 to 430nm, but the reaction product, 2,6-diamino-8-azapurine, emits in a different spectral region (λmax∼363nm) with nearly 40% yield, providing a strong fluorogenic effect at 350 to 360nm.