▁de pro ton ates ▁the ▁alco hol ▁to ▁increase ▁its ▁react ivity ▁as ▁a ▁nucle oph ile . ▁ ▁Catal ysis ▁takes ▁place ▁in ▁two ▁steps : ▁ ▁First ly ▁the ▁nucle oph ile ▁attacks ▁the ▁substr ate ▁to ▁form ▁a ▁c oval ent ▁a cy l - enz yme ▁intermediate , ▁re le asing ▁the ▁first ▁product . ▁ ▁Second ly ▁the ▁intermediate ▁is ▁hydro ly sed ▁by ▁water ▁to ▁reg ener ate ▁the ▁free ▁en zym e ▁and ▁release ▁the ▁second ▁product . ▁ ▁In ▁orn ith ine ▁a cy l trans fer ase , ▁instead ▁of ▁water , ▁the ▁substr ate ▁orn ith ine ▁( the ▁accept or ) ▁performs ▁the ▁second ▁nucle oph il ic ▁attack ▁and ▁so ▁leaves ▁with ▁the ▁a cy l ▁group . ▁ ▁Classification ▁and ▁evolution ▁ ▁Five ▁families ▁belonging ▁to ▁two ▁separate ▁super famil ies ▁are ▁currently ▁recogn ised : ▁the ▁N tn ▁fol d ▁prote os om es ▁( super family ▁P B ) ▁and ▁the ▁DOM ▁fol d ▁orn ith ine ▁a cy l trans fer ases ▁( super family ▁P E ). ▁The ▁two ▁super famil ies ▁represent ▁two ▁independent , ▁conver gent ▁evolution s ▁of ▁the ▁same ▁active ▁site . ▁ ▁See ▁also ▁▁ ▁Prote ase ▁ser ine - ▁c yst e ine - ▁as part ic - ▁metal lo - ▁En zym e ▁Prote ol ysis ▁Catal yt ic ▁tri ad ▁Con ver gent ▁evolution ▁The ▁Prote ol ysis ▁Map ▁Prote ase ▁in hib itor ▁( ph arm ac