Properties: Double-strand-specific endonuclease that requires bivalent cations for maximal activity.
Activity: 10,000U/bottle according to Kunitz (+25°C; DNA as substrate).
Unit definition: One unit is the enzyme activity that causes an increase in the absorbance of 0.001 per minutes under assay conditions.
Double-strand-specific endonuclease that requires bivalent cations for maximal activity.
One unit, according to Kunitz, is the enzyme activity that under assay conditions causes an absorbance increase at 260 nm of 0.001/minute in 1 ml. Volume activity is determined in 0.1 M sodium acetate, 5 mM MgSO4, pH 5.0.
Assay mixture: Calf thymus DNA (100 μg) is incubated with 20 to 50 U DNase I at +25 °C.
The increase in absorbance is measured at 260 nm.
Information Note: These conditions are used for the determination of activity,according to Kunitz, since the Kunitz assay results in high reproducibility and sensitivity. When using this enzyme for normal experimental purposes, Roche recommends using incubation buffers that are appropriate for a given application, e.g., as mentioned in the standard literature (Sambrook et al., Curr. Prot. Mol. Biol., etc.).
Activator: The enzyme requires divalent cations for maximal activity. The specificity of the reaction depends on the nature of the cation used. In the presence of Mg2+ DNase I causes single-stranded nicks in dsDNA, while in the presence of Mn2+ the enzyme produces double-stranded breaks.
Storage conditions (working solution): Long-term Storage of the Dissolved Enzyme
The solvent generally recommended for DNase I is water. When DNase I is reconstituted in water, the solution can be kept for 2 days at 2 to 8 °C and for 1 month at -15 to -20 °C. For best results, prepare appropriate aliquots and avoid repeated freezing and thawing. However, for long-term storage, carefully dissolve DNase I in one of the buffers listed below. In buffer 1, the enzyme will be stable for several weeks. The enzyme will be stable for at least 18 months if it is dissolved in buffer 2, 3, or 4 and stored at the recommended temperatures.
Information note: Do not vortex the enzyme while dissolving!
Buffer 1: 20 mM Tris-HCl, 20 mM MgCl2, 5 mM CaCl2, 0.1 mM dithioerythritol, 0.1 mM EDTA, 50% (v/v) glycerol, pH 8. Store this solution at -15 to-25 °C; it will not freeze at this temperature and will be stable for several weeks.
Buffer 2: 20 mM Tris-HCl, 50 mM NaCl, 1 mM dithioerythritol, 100 μg/mL BSA, 50% glycerol (v/v), pH 7.6. Store this solution at -15 to -25 °C for up to 18 months; it will not freeze at this temperature.
Buffer 3: 20 mM Tris-HCl, 1 mM MgCl2, 50% (w/v) glycerol, pH 7.5. Store this solution at -15 to -25 °C for up to 18 months; it will not freeze at this temperature.
Buffer 4: 20 mM Tris-HCl, 1 mM MgCl2, pH 7.5. Aliquot in appropriate amounts (e.g., 10 μl), freeze the aliquots quickly on dry ice, and store at -60 °C or below for up to 18 months. Thaw only the amount needed for each experiment. Do not refreeze. Discard any leftover thawed solution.