KINETIC-PROPERTIES OF ADENINE-NUCLEOTIDE ANALOGS AGAINST PURIFIED 5-PHOSPHORIBOSYL-1-PYROPHOSPHATE SYNTHETASES FROM ESCHERICHIA-COLI, RAT-LIVER AND HUMAN ERYTHROCYTES

The nucleoside analogue 2',3'-dideoxyadenosine (ddA), the phosphonate isostere of 2',3'-dideoxy-2',3'-didehydro-adenosine (d4A) 5'-monophosp hate (d4API), and the acyclic nucleoside phosphonates PMEoA, PMEA, FPM PA and PMPA are potent and selective antiretroviral agents. We found t hat these compounds are recognized as substrates by the PRPP synthetas es from E. coli, rat liver and human erythrocytes, as their monophosph ate and triphosphate form in the reverse and forward reaction, respect ively. In particular, ddA-5'-monophosphate (ddAMP) and ddA-5'-triphosp hate proved to be excellent substrates for the enzymes. D4API was a re latively good substrate of the rat liver and human erythrocyte PRPP sy nthetases. The acyclic nucleoside phosphonates were rather poor substr ates, as evident from their low V-max values. None of the PRPP synthet ases are found to act stereospecifically: they recognized both the S- and R-enantiomers of FPMPA and PMPA in a comparably efficient manner. Our data indicate that PRPP synthetase may recognize a much broader ra nge of adenine nucleotide analogues than previously thought.