▁R NA ), ▁which ▁catal y zes ▁the ▁cle av age ▁of ▁a ▁specific ▁ph osph odi ester ▁bond . ▁It ▁was ▁discovered ▁using ▁an ▁in - v it ro ▁evolution ▁study ▁where ▁the ▁research ers ▁were ▁selecting ▁for ▁R N As ▁that ▁specifically ▁cle aved ▁themselves ▁in ▁the ▁presence ▁of ▁lead . ▁However , ▁since ▁then , ▁it ▁has ▁been ▁discovered ▁in ▁several ▁natural ▁systems . ▁Le ad zym e ▁was ▁found ▁to ▁be ▁efficient ▁and ▁dynamic ▁ ▁in ▁the ▁presence ▁of ▁mic rom olar ▁concentr ations ▁of ▁lead ▁ ions . ▁Un like ▁in ▁other ▁small ▁self - cle aving ▁rib oz ym es , ▁other ▁div al ent ▁metal ▁ ions ▁cannot ▁replace ▁P b 2 + ▁in ▁the ▁lead zym e . ▁Due ▁to ▁oblig atory ▁requirement ▁for ▁a ▁lead , ▁the ▁rib oz yme ▁is ▁called ▁a ▁met all or ib oz yme . ▁ ▁Le ad zym e ▁has ▁been ▁subject ed ▁to ▁extensive ▁bio chem ical ▁and ▁struct ural ▁character ization . ▁The ▁minimal ▁secondary ▁structure ▁of ▁lead zym e ▁is ▁surprising ly ▁very ▁simple ▁. ▁It ▁compr ises ▁an ▁asym metric ▁internal ▁loop ▁composed ▁of ▁six ▁nucle ot ides ▁and ▁a ▁hel ical ▁region ▁on ▁each ▁side ▁of ▁the ▁internal ▁loop . ▁The ▁cle av age ▁site ▁of ▁lead zym e ▁is ▁located ▁within ▁a ▁four - n uc le ot ide ▁long ▁asym metric ▁internal ▁loop ▁that ▁also ▁consists ▁of ▁R NA ▁hel ices ▁on ▁its ▁both ▁sides . ▁This ▁is ▁shown ▁in ▁top