Identification of Intermediates in Peroxidase Catalytic Cycle of a DNAzyme Possessing Heme

Heme in the ferric state (heme(Fe3+)) binds to G-quadruplex DNAs to form stable complexes that exhibit enhanced peroxidase activities. The complexes are considered DNAzymes possessing heme as a prosthetic group (heme-DNAzymes), and have been extensively investigated as promising catalysts for a variety of applications. On ESR and stopped-flow measurements, an iron(IV)oxo porphyrin pi-cation radical known as Compound I was detected in reaction mixtures of heme-DNAzymes and hydrogen peroxide. This finding not only resolved the long-standing issue of the mechanism underlying the enhancement of the peroxidase activity of heme(Fe3+) in the scaffold of a G-quadruplex DNA, but also provided new insights as to the design of novel heme-DNAzymes.