Determination of the activity of catalase using a europium(III)–tetracycline-derived fluorescent substrate (original) (raw)
2003, Analytical Biochemistry
A one-step method is described for the fluorometric determination of the activity of the enzyme catalase (EC 1.11.1.6.), based on the finding that H 2 O 2 in the europium (III)-tetracycline-hydrogen peroxide system is consumed by catalase. This is accompanied by a large decrease in both fluorescence intensity and decay time. The limit of detection (LOD; at S=N ¼ 3) for catalase at 30°C for a 10-min kinetic assay is 1.0 unit/mL, with a linear range from 1.0 to 10 unit/mL. At an incubation time of 30 min at 37°C for a onepoint assay, the LOD is 0.046 unit/mL, with a linear range from 46 to 400 munit/mL. The assay was performed on microtiterplates and is fully compatible with existing plate readers. It is a one-step, simple, and sensitive method suitable for both continuous kinetic and one-point detections, does not require the addition of other substrates, and works best at neutral pH (with an optimum at pH 6.9). The reagent has the typical spectral features of a europium-ligand complex including a large Stokes shift (210 nm), a red linelike emission (centered at 616 nm), and a decay time in the microsecond domain. It is also the first europium-based probe that is compatible with the 405-nm diode laser. In summary, the new assay provides distinct advantages over direct ultraviolet detection and over the two-reagent (peroxidase) method.
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