▁L ys ▁at ▁resid ue ▁ 1 2 5 ▁and ▁Le u ▁for ▁Asp ▁at ▁resid ue ▁ 1 0 8 ▁significantly ▁decre ased ▁DNA ▁binding ▁and ▁the ▁catal yt ic ▁function ▁of ▁H ind III . ▁ ▁In ▁a ▁separate ▁mut agen esis ▁study ▁it ▁was ▁shown ▁that ▁a ▁mut ation ▁at ▁resid ue ▁ 1 2 3 ▁from ▁Asp ▁to ▁As n ▁reduced ▁en zym atic ▁activity . ▁ ▁Despite ▁the ▁fact ▁that ▁this ▁resid ue ▁is ▁most ▁likely ▁responsible ▁for ▁the ▁unw inding ▁of ▁DNA ▁and ▁coord ination ▁to ▁water ▁rather ▁than ▁direct ▁interaction ▁with ▁the ▁attack ing ▁nucle oph ile , ▁its ▁specific ▁function ▁is ▁unknown . ▁ ▁Pro posed ▁mechanism ▁ ▁While ▁restriction ▁en zym es ▁cle ave ▁at ▁specific ▁DNA ▁sequences , ▁they ▁are ▁first ▁required ▁to ▁bind ▁non - specific ally ▁with ▁the ▁DNA ▁back bone ▁before ▁local izing ▁to ▁the ▁restriction ▁site . ▁ ▁On ▁average , ▁the ▁restriction ▁en zym e ▁will ▁form ▁ 1 5 - 2 0 ▁hydro gen ▁b onds ▁with ▁the ▁bases ▁of ▁the ▁recognition ▁sequence . ▁ ▁With ▁the ▁aid ▁of ▁other ▁van ▁der ▁Wa als ▁interactions , ▁this ▁bond ing ▁facil it ates ▁a ▁conform ational ▁change ▁of ▁the ▁DNA - enz yme ▁complex ▁which ▁leads ▁to ▁the ▁activation ▁of ▁catal yt ic ▁cent ers . ▁ ▁Despite ▁the ▁lack ▁of ▁evidence ▁suggesting ▁an ▁exact ▁mechanism ▁for ▁the ▁cle av age ▁of ▁DNA ▁by ▁H ind III , ▁site - mut agen esis ▁analysis ▁couple d ▁with ▁more