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 λ max ∼ 425 to 430 nm, but the reaction product, 2,6-diamino-8-azapurine, emits in a different spectral region ( λ max ∼ 363 nm) with nearly 40% yield, providing a strong fluorogenic effect at 350 to 360 nm.