The role of 2', 3'‐cyclic phosphodiesters in the bovine pancreatic ribonuclease A catalysed cleavage of RNA: intermediates or products?

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Abstract
There is a considerable degree of ambiguity in the literature regarding the role of the 2',3'‐cyclic phosphodiesters formed during the reaction of RNA cleavage catalysed by ribonuclease. Usually the reaction is considered to take place in two steps: in the first step there is a transphosphorylation of the RNA 3',5'‐phosphodiester bond broken yielding a 2',3'‐cyclic phosphodiester which in the second step is hydrolysed to a 3'‐nucleotide. Although in many occasions, either explicitly or implicitly, the reaction is treated as taking place sequentially, this is not the case as it has been shown that the 2',3'‐phosphodiesters are actually released to the medium as true products of the reaction and that no hydrolysis of these cyclic compounds takes place until all the susceptible 3',5'‐phosphodiester bonds have been cyclised. Comparison of the hydrolysis and alcoholysis of the 2',3'‐phosphodiesters catalysed by RNase A indicates that the hydrolysis reaction has to be considered formally as a special case of the transphosphorylation back reaction in which the R group of the R‐OH substrate is just H. It is thus concluded that the 2',3'‐cyclic phosphodiesters formed in the ribonuclease A reaction are true products of the transphosphorylation reaction and not intermediates as usually considered.

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