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 X(n)G(m)X(p) sequences (X=A, T or C), especially T(n)G(m)T(p) 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 Hg(2+) detection method was developed.