. ▁More ▁specifically , ▁T yr - 1 4 ▁and ▁Asp - 9 9 ▁di pol es ▁work ▁to ▁stabil ize ▁the ▁growing ▁charge ▁which ▁accum ul ates ▁on ▁the ▁en olate ▁o xygen ▁( O - 3 ) ▁throughout ▁catal ysis . ▁ ▁In ▁a ▁similar ▁way , ▁the ▁charge ▁on ▁Asp 3 8 ▁is ▁stabil ized ▁by ▁surrounding ▁resid ues ▁and ▁a ▁water ▁mole c ule ▁during ▁the ▁course ▁of ▁the ▁reaction . ▁ ▁The ▁Box er ▁group ▁used ▁experimental ▁St ark ▁spect ro sc opy ▁methods ▁to ▁identify ▁the ▁presence ▁of ▁H - b ond - medi ated ▁electric ▁fields ▁within ▁the ▁K SI ▁active ▁site . ▁ ▁These ▁measurements ▁quant ified ▁the ▁electro static ▁contribution ▁to ▁K SI ▁catal ysis ▁( 7 0 %). ▁ ▁The ▁active ▁site ▁is ▁l ined ▁with ▁hydro ph ob ic ▁resid ues ▁to ▁accommod ate ▁the ▁substr ate , ▁but ▁Asp - 9 9 ▁and ▁T yr - 1 4 ▁are ▁within ▁hydro gen ▁bond ing ▁distance ▁of ▁O - 3 . ▁ ▁The ▁hydro gen ▁b onds ▁from ▁T yr - 1 4 ▁and ▁Asp - 9 9 ▁are ▁known ▁to ▁significantly ▁affect ▁the ▁rate ▁of ▁catal ysis ▁in ▁K SI . ▁Mut agen esis ▁of ▁this ▁resid ue ▁to ▁al an ine ▁( D 9 9 A ) ▁or ▁as par agine ▁( D 9 9 N ) ▁results ▁in ▁a ▁loss ▁in ▁activity ▁at ▁p H ▁ 7 ▁of ▁ 3 0 0 0 - fold ▁and ▁ 2 7