Some cleave only double-stranded DNA, others are specific for single-stranded molecules, and still others are active toward both.
Other types of DNase include Micrococcal nuclease.
DNA absorbs UV light with a wavelength of maximal absorbance near 260 nm. This absorption is due to the pi electrons in the aromatic bases of the DNA. In dsDNA, or even regions of RNA where double stranded structure occurs, the bases are stacked parallel to each other and the overlap of the base molecular orbitals leads to a decrease in absorbance of UV light. This phenomenon is called the hyperchromic effect. When DNAse liberates nucleotides from dsDNA, the bases are no longer stacked like they are in dsDNA, so that orbital overlap is minimized and UV absorbance increases. This increase in absorbance underlies the basis of Kunitz unit of DNAse activity. One Kunitz unit is defined as the amount of enzyme that causes an increase in absorbance at 260 nm of 0.001 per mL when acting upon highly polymerized DNA at 25 C and pH 5.0 under specified conditions. A standard enzyme preparation should be run in parallel with an unknown because standardization of DNA preparations and their degree of polymerization in solution is not possible.
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