On the mechanism of catalysis by ribonuclease: Cleavage and isomerization of the dinucleotide UpU catalyzed by imidazole buffers

Article abstract of DOI:10.1021/ja00194a050

Uridylyl(3',5')uridine [(3',5')-UpU] undergo cleavage to uridine 2',3'-cyclic phosphate and uridine, catalyzed by imidazole buffers. Kinetic studies indicate a sequential bifunctional mechanism, with one buffer component catalyzing its forward decomposition to products. From a study of the buffer-catalyzed isomerization of (3',5')-UpU to [2',5']-UpU, the first catalyst is identified as imidazolium ion and the second as imidazole. The resulting detailed mechanism is chemically reasonable. It is also consistent with what is known about bovine pancreatic ribonuclease. Thus, a related multistep mechanism is suggested for the enzymatic reactions as well.