AFFINITY OF GUANOSINE DERIVATIVES FOR POLYCYTIDYLATE REVISITED

Evidence is presented for complexation of guanosine 5'-monophosphate 2 -methylimidazolide (2-MeImpG) with polycytidylate (poly(C)) at pH 8.0 and 23 degrees C in the presence of 1.0 M NaCl and 0.2 M MgCl2 in wate r. The association of 2-MeImpG with poly(C) was investigated using UV- vis spectroscopy as well as by monitoring the kinetics of the nucleoph ilic substitution reaction of the imidazole moiety by amines. The resu lts of both methods are consistent with moderately strong poly(C). 2-M eImpG complexation and the spectrophotometric measurements allowed the construction of a binding isotherm with a concentration of 2-MeImpC e qual to 5.55 +/- 0.15 mM at half occupancy. UV spectroscopy was employ ed to establish the binding of other guanosine derivatives on poly(C). These derivatives are guanosine 5'-monophosphate (5'GMP), guanosine 5 '-monophosphate imidazolide (ImpG), and guanosine 5'-monophosphate mor pholidate (morpG). Within experimental error these guanosine derivativ es exhibit the same affinity for poly(C) as 2-MeImpG.