family . ▁Despite ▁being ▁considered ▁hyd rol ases ▁with ▁poor ▁substr ate ▁turn over , ▁an ▁int act ▁catal yt ic ▁tri ad ▁is ▁required ▁for ▁the ▁protein ' s ▁bi ological ▁function . ▁Several ▁( in ▁part ▁compet ing ) ▁models ▁have ▁been ▁proposed ▁for ▁the ▁invol vement ▁of ▁the ▁catal yt ic ▁tri ad ▁in ▁lig and ▁per ception : ▁▁ ▁H ydro ly s is ▁of ▁str ig ol act one , ▁resulting ▁in ▁the ▁D - ring ▁being ▁c oval ently ▁attached ▁to ▁the ▁active ▁site ▁ser ine . ▁ ▁H ydro ly s is ▁of ▁str ig ol act one , ▁resulting ▁in ▁a ▁free ▁D - ring ▁that ▁serves ▁as ▁a ▁mole cular ▁gl ue ▁at ▁the ▁entrance ▁of ▁the ▁re ceptor , ▁medi ating ▁interaction ▁with ▁another ▁protein . ▁ ▁Binding ▁of ▁non - h ydro ly zed , ▁int act ▁str ig ol act one ▁that ▁generates ▁an ▁alter ed ▁D W AR F 1 4 ▁protein ▁surface , ▁medi ating ▁interaction ▁with ▁another ▁protein . ▁ ▁H ydro ly s is ▁of ▁str ig ol act one , ▁resulting ▁in ▁the ▁D - ring ▁being ▁c oval ently ▁attached ▁to ▁the ▁active ▁site ▁hist id ine . ▁ ▁H ydro ly s is ▁of ▁str ig ol act one , ▁resulting ▁in ▁the ▁D - ring ▁being ▁c oval ently ▁attached ▁to ▁the ▁active ▁site ▁ser ine ▁and ▁hist id ine ▁at ▁the ▁same ▁time , ▁indu cing ▁a ▁conform ational ▁change ▁of ▁D