Proteinase K is one of the most active endopeptidases known. It rapidly inactivates endogenous nucleases including RNases and DNases making it suitable for the degradation of proteins during the isolation and manipulation of RNA and DNA. Proteinase K may also be used to permeabilize cells and tissues prior to labeling with in situ Apoptosis Detection Kits. Permeabilization of the sample by Proteinase K creates pores in the cell membrane and facilitates access to the DNA by biotinylated dNTPS.