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Deoxyribonuclease (DNase)

(Deoxyribonucleate 5'-oligonucleotidohydrolase; EC

Deoxyribonuclease (DNase I), from bovine pancreas, is an endonuclease catalyzing the hydrolysis of phosphodiester linkages, adjacent to a pyrimidine nucleotide yielding 5'phosphate terminated polynucleotides. The enzyme is able to act upon single as well as double-stranded DNA and on chromatin.

The DNase from bovine pancreas exists in multiple forms (Salnikow, J., Moore, S.; and W.H. Stein, J Biol Chem, 254, 5685, 1970) with DNase A being the predominant form (Salnikow, J.; Liao, T.M.; Moore, S. and W.H. Stein, J. Biol Chem, 248, 1480, 1973). In addition to bovine pancreas, DNase activity has also been demonstrated in other mammalian tissues (Durphy, M; Manly, P.N. and E.C. Friedburg, J. Cell. Biol, 62, 695, 1975).

1.Source: Bovine Spleen
   Form: Freeze-dried powder 
   Solubility: Distilled water or dilute buffer 
   Stability: Store at -20 C (-4 F) 
   Activity (approx.): 200 U/mg protein 
   Protein (approx.): 90% (biuret) 
   Catalog No.: 150A0200 

The amount of enzyme which results in an increase in absorbance at 260 nm and 0.001 per minute per ml at 25°C at pH 5.00.

The assay method is a modification of the method of Kunitz (Kunitz, M., J. Gen Physiol, 33, 349, 1950). An increase in absorbance at 260 nm, caused by the depolymerization of DNA by the enzyme, is a measure of enzyme activity.

  1. 1.00 M Acetate Buffer, pH 5.00.
  2. 0.05 M Magnesium sulfate.
  3. Substrate: 4 mg DNA/100 ml solution. (Dissolve 4 mg of highly polymerized DNA in 50 ml of distilled water, add 10 ml acetate buffer and 10 ml magnesium sulfate. Dilute to 100 ml with distilled water.) The substrate will be stable for 2 weeks if stored at 4°C.
  4. Enzyme - dissolved in acetate buffer to yield a final concentration of 40-60 U/ml.

  1. Set spectrophotometer (equipped with a strip chart recorder and temperature control) at 260 nm and 25°C.
  2. In quartz cuvettes pipette the following at 25°C:
                                 TEST         CONTROL 
    Substrate                    3.0 ml        3.0 ml 
    Distilled water                            1.0 ml 
    Enzyme @ zero time           1.0 ml
    Record the rate of increase in absorbance at 260 nm for approximately 8 min. after the initial lag time of approximately 15 min.

Activity (U/mg) = (ΔE260nm/min)(1000)
(mg Enz./ml)

Note: As the degree of polymerization of DNA varies it is necessary to assay a standard DNase and a correction factor is applied for calculating the activity of the test enzyme.

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