Purine riboside-5'-O-triphosphate sodium, an active metabolite of Nebularine , acts as an inhibitor of DNA primase ATP and GTP polymerization activities, with IC 50 values of 35 µM and 28 µM for the human enzyme , respectively. Purine riboside-5'-O-triphosphate sodium inhibits calmodulin-dependent protein kinase II (CaMKII) with a K i value of 590 µM.