Faster rates with less catalyst in template-directed reactions

We have recently shown that the polycytidylic acid-directed polymerization of guanosine 5'-monophosphate 2-methylimidazolide (2-MeImpG) is amenable to kinetic study and that rate determinations as a function of 2-MeImpG concentration can reveal much mechanistic detail (Kanavarioti et al. 1993). Here we report kinetic data which show that, once the reaction has been initiated by the formation of dimers, the elongation of dimers to form longer oligomers is accelerated by decreasing polycytidylate (poly(C)) concentration from 0.05 to 0.002 M. This result is consistent with the previously proposed mechanism. The increase in the observed pseudo-first order rate constant for formation of the trimer, k3', and the corresponding constant for formation of oligomers longer than the trimer, ki' (ki' is independent of oligomer length for i > or = 4), with decreasing template concentration for a given monomer concentration is attributed to an increase in template occupancy as template concentration is reduced.