  A realistic physical model for the so called rate promoting vibration (RPV)
at enzyme action is constructed. The origin of the RPV is assumed to be an
oscillating electric field produced by long-lived localized vibrational modes
in protein dynamics, namely, by the so called discrete breather (DB) in
secondary structure. The strength of interaction of the RPV with the reaction
coordinate is evaluated and its effect on the reaction acceleration is assessed
within the framework of modern theory for thermally activated escape rate at
periodic driving. We reveal the phenomenon of resonant activation in our model
elucidating why the frequency of the RPV in the range $100\div200 cm^{-1}$ was
chosen by the evolution of enzymes as an optimal one. The effect of the RPV on
the reaction acceleration is shown to vary from moderate one (up to
$10^3\div10^4$) in the case of three-site DB to enormous (up to $10^6\div10^8$)
in the case of five-site DB and thus can significantly contribute into enzyme
catalytic efficiency. Also the model is shown to be compatible with the known
functional dependence of enzymatic reaction rates on solvent viscosity.
