. ▁This ▁mode ▁of ▁catal ysis ▁is ▁similar ▁to ▁how ▁rib on uc leases ▁( prote ins ) ▁function ▁rather ▁than ▁any ▁known ▁small ▁self - cle aving ▁rib oz yme . ▁ ▁The ▁lead zym e ▁is ▁thought ▁to ▁have ▁a ▁highly ▁dynamic ▁structure . ▁Many ▁studies ▁including ▁N MR , ▁X - ray ▁cry stal log raph y ▁and ▁mole cular ▁model ing ▁have ▁revealed ▁slightly ▁different ▁structures . ▁Rec ently ▁using ▁time - resol ved ▁spect ro sc opy , ▁it ▁was ▁shown ▁that ▁the ▁active ▁site ▁of ▁lead zym e ▁is ▁very ▁dynamic . ▁It ▁samples ▁a ▁lot ▁of ▁different ▁conform ations ▁in ▁solution ▁and ▁that ▁the ▁delta ▁G ▁of ▁the ▁inter con version ▁between ▁different ▁conform ations ▁is ▁very ▁low . ▁Cons istent ▁with ▁these ▁studies , ▁a ▁high - resol ution ▁cry stal ▁structure ▁also ▁revealed ▁two ▁distinct ▁conform ations ▁of ▁the ▁lead zym e ▁with ▁different ▁binding ▁sites ▁for ▁M g 2 + ▁and ▁Sr 2 + ▁( P b 2 + ▁subst it utes ) ▁in ▁the ▁two ▁conform ations . ▁In ▁the ▁ground ▁state , ▁lead zym e ▁bind s ▁a ▁single ▁Sr 2 + ▁ion ▁at ▁nucle ot ides ▁G 4 3 , ▁G 4 5 ▁and ▁A 4 5 . ▁This ▁binding ▁site ▁is ▁away ▁from ▁the ▁sc iss ile ▁bond ▁( cle av age ▁site ) ▁and ▁thus ▁does ▁not ▁explain ▁the ▁invol vement ▁of ▁the ▁P b 2 + ▁in ▁the ▁catal ysis . ▁However , ▁in ▁the ▁second ▁con