Assay for measuring the enzyme activity of PE-DNase I/Pt

One Kunitz unit of DNase I is defined as the amount of enzyme added to plasmid PX330 that causes an increase (0.001 per minute) in absorbance at the wavelength of 260 nm in the reaction buffer [40 mM tris-HCl, 2.5 mM MgSO4, and 1 mM CaCl2 (pH 8.0)]. In a typical assay, 10 mg of PE-DNase I/Pt in 0.5 ml of reaction buffer and 0.5 ml of plasmid PX330 (100 μg/ml) in reaction buffer were mixed together. The reaction was performed at 25 or 45°C for 20 min and then terminated by adding 100 μl of EDTA (20 mM). Then, the reaction solution was centrifuged (8000 rpm, 5 min) at 4°C. The absorbance of the supernatant at 260 nm was measured by NanoDrop 2000 (Thermo Fisher Scientific, USA).

In the assay under NIR irradiation, the reaction was performed at room temperature. The mix of PE-DNase I/Pt and plasmid PX330 was irradiated by an NIR laser at 3.8 W cm−2 for 20 min, and then, the same procedure was conducted as described above.

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