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Izunokuni, Japan

Watabe S.,BL Co. | Kodama H.,Tokushima Bunri University | Kaneda M.,Tokushima Bunri University | Morikawa M.,Tokushima Bunri University | And 6 more authors.
Biophysics (Japan) | Year: 2014

An ultrasensitive method for the determination of proteins is described that combines an enzyme-linked immunosorbent assay (ELISA) and a thionicotinamide-adenine dinucleotide (thio-NAD) cycling method. A sandwich method using a primary and a secondary antibody for antigens is employed in an ELISA. An androsterone derivative, 3α-hydroxysteroid, is produced by the hydrolysis of 3α-hydroxysteroid 3-phosphate with alkaline phosphatase linked to the secondary antibody. This 3α-hydroxysteroid is oxidized to a 3-ketosteroid by 3α-hydroxysteroid dehydrogenase (3α-HSD) with a cofactor thio-NAD. By the opposite reaction, the 3-ketosteroid is reduced to a 3α-hydroxysteroid by 3α-HSD with a cofactor NADH. During this cycling reaction, thio-NADH accumulates in a quadratic function-like fashion. Accumulated thio-NADH can be measured directly at an absorbance of 400 nm without any interference from other cofactors. These features enable us to detect a target protein with ultrasensitivity (10–19 mol/assay) by measuring the cumulative quantity of thio-NADH. Our ultrasensitive determination of proteins thus allows for the detection of small amounts of proteins only by the application of thio-NAD cycling reagents to the usual ELISA system. © 2014 THE BIOPHYSICAL SOCIETY OF JAPAN.


Ito E.,Tokushima Bunri University | Watabe S.,BL Co. | Morikawa M.,Tokushima Bunri University | Kodama H.,Tokushima Bunri University | And 2 more authors.
Methods in Enzymology | Year: 2013

Fluorescence correlation spectroscopy (FCS) is a technique in which measurement of fluorescence intensity fluctuations is used to clarify dynamic molecular interactions within a very small space in a solution containing a small number of fluorescent molecules. The FCS-based analysis gives the average number and average diffusion time of the fluorescent molecules during their passage through a very small space. One advantage of FCS is that physical separation between free and bound fluorescent probes is not required because the properties of fluorescence fluctuations are accounted for. Therefore, when fluorescent probes are bound with proteins by peroxidase and hydrogen peroxide (H2O2), FCS enables us to detect H2O 2 with high sensitivity. In addition, because H2O 2 is generated by oxidase-catalyzed reactions, a highly sensitive method for detecting H2O2 is applicable to the measurement of low levels of various oxidases and their substrates, such as glucose. We here describe the protocol of a de novo, highly sensitive method for the measurement of H2O2 and glucose using FCS. © 2013 Elsevier Inc. All rights reserved.


Watabe S.,BL Co. | Sakamoto Y.,Tokushima Bunri University | Morikawa M.,Tokushima Bunri University | Okada R.,Tokushima Bunri University | And 2 more authors.
PLoS ONE | Year: 2011

Background: Because H 2O 2 is generated by various oxidase-catalyzed reactions, a highly sensitive determination method of H 2O 2 is applicable to measurements of low levels of various oxidases and their substrates such as glucose, lactate, glutamate, urate, xanthine, choline, cholesterol and NADPH. We propose herein a new, highly sensitive method for the measurement of H 2O 2 and glucose using fluorescence correlation spectroscopy (FCS). Methodology/Principal Findings: FCS has the advantage of allowing us to determine the number of fluorescent molecules. FCS measures the fluctuations in fluorescence intensity caused by fluorescent probe movement in a small light cavity with a defined volume generated by confocal illumination. We thus developed a highly sensitive determination system of H 2O 2 by FCS, where horseradish peroxidase (HRP) catalyzes the formation of a covalent bond between fluorescent molecules and proteins in the presence of H 2O 2. Our developed system gave a linear calibration curve for H 2O 2 in the range of 28 to 300 nM with the detection limit of 8 nM. In addition, by coupling with glucose oxidase (GOD)-catalyzed reaction, the method allows to measure glucose in the range of 80 nM to 1.5 μM with detection limit of 24 nM. The method was applicable to the assay of glucose in blood plasma. The mean concentration of glucose in normal human blood plasma was determined to be 4.9 mM. Conclusions/Significance: In comparison with commercial available methods, the detection limit and the minimum value of determination for glucose are at least 2 orders of magnitude more sensitive in our system. Such a highly sensitive method leads the fact that only a very small amount of plasma (20 nL) is needed for the determination of glucose concentration in blood plasma. © 2011 Watabe et al.


Iwai A.,Hokkaido University | Yoshimura T.,Health Sciences University of Hokkaido | Wada K.,Health Sciences University of Hokkaido | Watabe S.,BL Co. | And 3 more authors.
Analytical Sciences | Year: 2013

A simple spectrophotometric method for the assay of steroid 5α-reductase (5α-sr) was developed in which 5α-dihydrotestosterone (5α-dht) and 5α-androstane-3α,17β-diol (5α-diol), metabolites formed in the nadph-dependent reduction of testosterone with enzyme sources of 5α-sr, were measured by enzymatic cycling using 3α-hydroxysteroid dehydrogenase in the presence of excess thionicotinamide-adenine dinucleotide (thio-nad) and nadh. it was found that 5α-sr activity was proportional to the accumulated thio-nadh having an absorption maximum at 400 nm. because of the high cycling rate (>600 cycle per min) and no interference from testosterone, enzymatic cycling can determine the sum of 5α-dht and 5α-diol at the picomole level without separation from excess testosterone. the present method was readily applicable to the assay of 5α-sr activity of rat liver and prostate microsomes as well as to the assay of inhibitory activity of finasteride, a synthetic inhibitor of 5α-sr. ©2013 The Japan Society for Analytical Chemistry.


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