Studies of this reaction in multiple ribozymes have served to establish that the reaction chemistry (catalytic mechanism) is an endogenous property of the RNA molecule itself and is not mediated by metal ions, as is true for some protein enzymes and some other ribozymes. Moreover, cleavage activity is still observed when Mg2+ is replaced by [Co(NH3)6]3+. Co3+ binds NH3 so tightly in solution that NH3 does not dissociate to any appreciable extent, and therefore does not become protonated. This suggests there is no metal-catalyzed proton transfer or direct coordination to the RNA, but instead metals are only required for folding. Furthermore, in crystal structures of a ribozyme-inhibitor complex and a transition state mimic, it was shown that the three-dimensional architecture splays apart A-1 and G+1, positioning the 2'-OH of A-1 for an in-line nucleophilic attack on the scissile phosphate linkage. Additionally, G8, A38, and A9 have been suggested to play roles in the catalysis by deprotonating the 2'-OH of A-1, stabilizing the developing negative charge of the pentacoordinate phosphate oxygens, and protonating the 5'-O leaving group of G+1.
