Effect of inhibitors on the montmorillonite clay-catalyzed formation of RNA: Studies on the reaction pathway

The Langmuir adsorption isotherms of the phosphoroimidazolides of adenosine (ImpA) and uridine (ImpU), dA(5') ppdA and N-6, N-6-dimethyladenine bindin g on montmorillonite are consistent with their forming a monolayer on the c lay surface. This suggests the condensation of ImpA and ImpU to oligomers p roceeds on the surface of the clay and not in groups of monomers stacked on the clay surfaces. The binding and reactions of ImpU and ImpA on montmoril lonite are blocked by N-6, N-6-dimethyladenine and dA(5') ppdA. dA(5') ppdA is a better inhibitor of oligomer formation than N-6, N-6-dimethyladenine because both adenine rings of dA(5') ppdA bind to the clay surface and bloc k adjacent catalytic sites. An upper limit of 5-10 x 10(15) catalytic sites on 50 mg of clay was estimated from the binding of ImpU and the inhibition of oligomer formation by dA(5') ppdA.