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. Author manuscript; available in PMC: 2016 Nov 1.
Published in final edited form as: Biochim Biophys Acta. 2015 Apr 30;1854(11):1801–1808. doi: 10.1016/j.bbapap.2015.04.022

Fig. 4.

Fig. 4

Transition state structures for nonenzymatic specific base catalysis (A) and for the enzymatic transition state model based on hydrogen bonding in the active site of the RNase A (B). The 2’O-P and 5’O-P bond lengths are indicated. For the RNase A transition state model the hydrogen bonds involving His119 and the 5’O, and His12 and a non-bridging oxygen are also indicated. The observed and calculated KIEs for the 2’O nucleophile (18kNUC), 5’O leaving group (18kLG) and non-bridging phosphoryl oxygens (18kNPO) are shown adjacent to the corresponding atoms in the transition state models. KIE values obtained for RNA and for uridine-m-nitrobenzyphosphate (UmNB) are labeled accordingly. Note that the computational results were obtained using a simplified ribose 3’-ethylphosphate model.