Peroxidase activity–structure relationship of the intermolecular four-stranded G-quadruplex–hemin complexes and their application in Hg2+ ion detection

The peroxidase activities of the complexes of hemin and intermolecular four-stranded G-quadruplexes formed by short-stranded XnGmXp sequences (X = A, T or C), especially TnGmTp sequences, were compared. The results, combining with those of circular dichroism (CD) spectra and acid–base transition study for DNA–hemin complexes, provide some important information about DNAzymes based on G-quadruplex–hemin complexes, such as the formation of a G-quadruplex structure is an important factor for determining whether a DNA sequence can enhance the catalytic activity of hemin; both intramolecular parallel G-quadruplexes and intermolecular four-stranded parallel G-quadruplexes can enhance the catalytic activity of hemin; the addition of T nucleotides to the 5′-end of a G-tract confers corresponding G-quadruplex greatly enhanced catalytic activity, whereas the addition of T nucleotides to the 3′-end of the G-tract has little effect; the high catalytic activity of hemin in the presence of some short-stranded G-rich sequences may be a result of the reduction of the acidity of the bound hemin cofactor. These studies provide more information for the DNA–hemin peroxidase model system, may help to elucidate the structure–function relationship of peroxidase enzymes and to develop novel, highly efficient peroxidase-liking DNAzymes. As a sequence of such an investigation, a new Hg2+ detection method was developed.