Raman difference spectroscopy is used to assess changes in the internal bonding of the oxygens of a ∅ VO2- group when that group is incorporated into a complex also involving RNase A, uridine, and a water molecule (the RNase/UVO2/H2O complex). We find that the strengths of the nonbridging V-O bonds are deceased by 0.055 vu and their bond lengths are decreased 0.012 Å, based on the stretching frequency changes of nonbridging V-O bonds upon formation of the enzymic RNase/UVO2/H2O complex from the cyclic vanadate diester in solution. The bond lengths are 1.638 Å for the solution complex and 1.650 Å for the enzymic complex. The values found for the bond lengths are about 0.15 Å shorter than those found previously in crystallographic studies. Assuming the RNase/UVO2/H2O adduct is a reasonably good transition state analogue, our Raman results suggest that the RNase-catalyzed hydrolysis of uridine 2',3'-cyclic phosphate proceeds via an S(N)2-like process. The process also may involve a small associative charactor, since the summed bond strength of nonbridging P-O bonds is reduced by only 0.11-0.22 vu in the transition state compared with the ground state, which means the summed bond strength of the PO bonds of the entering and leaving groups is correspondingly increased.
ASJC Scopus subject areas
- Colloid and Surface Chemistry