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), dA5' ppdA and N6,N6-dimethyladenine binding on montmorillonite are consistent with their forming a monolayer on the clay surface. This suggests the condensation of ImpA and ImpU to oligomers proceeds 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 montmorillonite are blocked by N6,N6-dimethyladenine and dA5' ppdA. dA5' ppdA is a better inhibitor of oligomer formation than N6,N6-dimethyladenine because both adenine rings of dA5' ppdA bind to the clay surface and block 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 dA5' ppdA.