... explana-tion for its poor excision by the enzyme. However, this stilldid not explain why the catalytic rate (Vmax) for U excisionin the U 2-hairpin is poor. For productive enzyme substrate complex formation, ... outÕform. Thereby, U may be spontaneously recognized by UDG. Recently, it has been shown that the excision of Ufrom such hairpin loops by UDG [2,3] is dependent on theU position in the loop. For ... the enzyme. Presumably, the potential energyrequired for these structural changes to occur before aproductive enzyme substrate complex is formed results inlower catalytic rates of U release...