Analysis Note
Protein determined by biuret.
Application
DNAse I is used to nick DNA as a first step to incorporate labeled bases into DNA. DNAse I from Sigma has been used along with other enzymes for tumor harvest and dissociation, during the isolation and molecular characterization of cancer stem cells in MMTV-Wnt-1 murine breast tumors.
Deoxyribonuclease I from bovine pancreas has been used in a study to determine that mammalian deoxyribonucleases I are classified into three types based on differences in their tissue concentrations. Deoxyribonuclease I from bovine pancreas has also been used in a study to compare the three primary structures of deoxyribonuclease isolated from bovine, ovine, and porcine pancreas.
Used for the removal of DNA from protein samples.
Biochem/physiol Actions
DNase I is an endonuclease that acts on phosphodiester bonds adjacent to pyrimidines to produce polynucleotides with terminal 5?-phosphates. In the presence of Mg2+, DNAse I cleaves each strand of DNA independently and the cleavage sites are random. Both DNA strands are cleaved at approximately the same site in the presence of Mn2+. The pH optimum is found to be between 7 and 8. Divalent cations such as Mn2+, Ca2+, Co2+, and Zn2+ are activators of the enzyme. A concentration of 5 mM Ca2+ stabilizes the enzyme against proteolytic digestion. DNAse I from bovine pancreas consists of four chromatographically distinguishable components, A, B, C, and D, with molar ratios being 4:1:1 respectively. Only minor amounts of D are found. 2-Mercaptoethanol, chelators, sodium dodecyl sulfate (SDS) and actin are known to inhibit the enzyme activity.
Packaging
1 vial in serum bottle
5 vials in serum bottle
Preparation Note
The enzyme powder may be reconstituted in water or any buffer at pH 4.0-9.0, except phosphate buffer. Calcium chelators should be avoided. 10 mg/mL solution of DNAse I in 0.15 M NaCl may lose ﹤10% of its activity when stored for a week in aliquots at −20 °C. The same solutions stored in aliquots at 2-8 °C can lose approximately 20% activity. It remains active for up to five hours at 60 °C between pH 5 and 7, and loses activity in ﹤10 minutes at 68 °C. It loses activity at the rate of 6%/hour in acetate buffer (pH 5.0) and tris buffer ((pH 7.2) at 1 mg/mL concentration.
Unit Definition
One Kunitz unit will produce a δA260 of 0.001 per min per mL at pH 5.0 at 25 °C, using DNA, Type I or III as substrate.
