Stereochemical studies of the beta-elimination reactions at aldehydic abasic sites in DNA: endonuclease III from Escherichia coli, sodium hydroxide, and Lys-Trp-Lys.

The DNA strand cleavage reaction catalyzed by endonuclease III from Escherichia coli (endo III) on the 3'-side of aldehyde abasic sites proceeds by a syn beta-elimination involving abstraction of the 2'-pro-S proton and formation of a trans alpha,beta-unsaturated aldose product; we previously reported the same stereochemical course for the reaction catalyzed by UV endonuclease V from bacteriophage T4 (UV endo V) [Mazumder, A., Gerlt, J. A., Rabow, L., Absalon, M. J., Stubbe, J., & Bolton, P. H. (1989) J. Am. Chem. Soc. 111, 8029-8030]. Since the UV endo V does not contain an 4Fe-4S center, the 4Fe-4S center present in endo III need not be assigned a unique role in the beta-elimination reaction. The beta-elimination reactions that occur under alkaline conditions (0.1 N NaOH) and in the presence of the tripeptide Lys-Trp-Lys proceed by anti beta-elimination mechanisms involving abstraction of the 2'-pro-R proton and formation of a trans alpha,beta-unsaturated aldose product. The different stereochemical outcomes of the enzymatic and nonenzymatic beta-elimination reactions support the hypothesis that the enzyme-catalyzed reactions may involve general-base-catalyzed abstraction of the 2'-pro-S proton by the internucleotidic phosphodiester leaving group.