Further studies on the buffer-catalyzed cleavage and isomerization of uridyluridine. Medium and ionic strength effects on catalysis by morpholine, imidazole, and acetate buffers help clarify the mechanisms involved and their relationship to the mechanism used by the enzyme ribonuclease and by a ribonuclease mimic

The cleavage and isomerization of 3',5'-uridyluridine catalyzed by morpholine buffers and by imidazole buffers, are examined. Findings prove the existence of a partitioning mechanism in which the buffer acid BH+ transforms the substrate to a phosphorane monoanion intermediate which then partitions either to the 2',5' isomer of the substrate or to the cleavage product. The negative catalytic effect of the buffer base on the isomerization reaction is not due to a medium effect. In fact, the medium effect on this reaction strengthens the catalytic evidence.