3 research outputs found
Hemin/G-Quadruplex-Catalyzed Aerobic Oxidation of Thiols to Disulfides: Application of the Process for the Development of Sensors and Aptasensors and for Probing Acetylcholine Esterase Activity
This
study describes the novel hemin/G-quadruplex DNAzyme-catalyzed
aerobic oxidation of thiols to disulfides and the respective mechanism.
The mechanism of the reaction involves the DNAzyme-catalyzed oxidation
of thiols to disulfides and the thiol-mediated autocatalytic generation
of H<sub>2</sub>O<sub>2</sub> from oxygen. The coupling of a concomitant
H<sub>2</sub>O<sub>2</sub>-mediated hemin/G-quadruplex-catalyzed oxidation
of Amplex Red to the fluorescent resorufin as a transduction module
provides a fluorescent signal for probing the catalyzed oxidation
of the thiol to disulfides and for probing sensing processes that
yield the hemin/G-quadruplex as a functional label. Accordingly, a
versatile sensing method for analyzing thiols (l-cysteine,
glutathione) using the H<sub>2</sub>O<sub>2</sub>-mediated DNAzyme-catalyzed
oxidation of Amplex Red to the resorufin was developed. Also, the l-cysteine and Amplex Red system was implemented as an auxiliary
fluorescent transduction module for probing recognition events that
form the catalytic hemin/G-quadruplex structures. This is exemplified
with the development of thrombin aptasensor. The thrombin/thrombin
binding aptamer recognition complex binds hemin, and the resulting
catalytic complex activates the auxiliary transduction module, involving
the aerobic oxidation of l-cysteine and the concomitant formation
of the fluorescent resorufin. Finally, the hemin/G-quadruplex DNAzyme/Amplex
Red system was used to follow the activity of acetylcholine esterase,
AChE, and to probe its inhibition. The AChE-catalyzed hydrolysis of
acetylthiocholine to the thiol-functionalized thiocholine enabled
the probing of the enzymatic activity of AChE through the hemin/G-quadruplex-catalyzed
aerobic oxidation of thiocholine to the respective disulfide and the
concomitant generation of the fluorescent resorufin product
Photoelectrochemical Biosensors Without External Irradiation: Probing Enzyme Activities and DNA Sensing Using Hemin/G-Quadruplex-Stimulated Chemiluminescence Resonance Energy Transfer (CRET) Generation of Photocurrents
A hemin/G-quadruplex nanostructure that is immobilized
on CdS quantum
dots (QDs) associated with an electrode leads, in the presence of
luminol, H<sub>2</sub>O<sub>2</sub>, and triethanolamine as an electron
donor, to the generation of photocurrents with no external irradiation
of the QDs. The hemin/G-quadruplex-catalyzed generation of chemiluminescence
leads to the chemiluminescence resonance energy transfer (CRET) to
the QDs, resulting in the photoexcitation of the QDs and the generation
of electron–hole pairs. The transfer of the conduction-band
electrons to the electrode, and the concomitant scavenging of the
valence-band holes by the triethanolamine electron donor result in
the generation of photocurrents. The CRET-stimulated generation of
photocurrents is applied to sense DNA by the labeling of the probe–analyte
complex with a hemin/G-quadruple, and is also implemented to follow
the activity of glucose oxidase and to sense glucose, by the labeling
of the enzyme with the hemin/G-quadruplex catalyst
Nucleoapzymes: Hemin/G-Quadruplex DNAzyme–Aptamer Binding Site Conjugates with Superior Enzyme-like Catalytic Functions
A novel concept to improve the catalytic
functions of nucleic acids (DNAzymes) is introduced. The method involves
the conjugation of a DNA recognition sequence (aptamer) to the catalytic
DNAzyme, yielding a hybrid structure termed “nucleoapzyme”.
Concentrating the substrate within the “nucleoapzyme”
leads to enhanced catalytic activity, displaying saturation kinetics.
Different conjugation modes of the aptamer/DNAzyme units and the availability
of different aptamer sequences for a substrate provide diverse means
to design improved catalysts. This is exemplified with (i) The H<sub>2</sub>O<sub>2</sub>-mediated oxidation of dopamine to aminochrome
using a series of hemin/G-quadruplex-dopamine aptamer nucleoapzymes.
All nucleoapzymes reveal enhanced catalytic activities as compared
to the separated DNAzyme/aptamer units, and the most active nucleoapzyme
reveals a 20-fold enhanced activity. Molecular dynamics simulations
provide rational assessment of the activity of the various nucleoapzymes.
The hemin/G-quadruplex–aptamer nucleoapzyme also stimulates
the chiroselective oxidation of l- vs d-DOPA by
H<sub>2</sub>O<sub>2</sub>. (ii) The H<sub>2</sub>O<sub>2</sub>-mediated
oxidation of <i>N</i>-hydroxy-l-arginine to l-citrulline by a series of hemin/G-quadruplex–arginine
aptamer conjugated nucleoapzymes