From Tritirachium album. Tissue fixation in formalin or other aldehyde solutions forms protein cross-links that mask the antigenic sites. This causes weak or false negative staining for immunohistochemical detection of certain proteins. The proteinase K based solution is designed to break the protein cross-links, therefore unmask the antigens and epitopes in formalin-fixed and paraffin-embedded tissue sections, thus enhancing staining intensity of antibodies. Proteinase K is a non-specific serine protease with a very high specific activity. It is therefore ideally suited for proteolytic digestion of formalin-fixed tissues. Proteinase K is active in the presence or absence of SDS, EDTA or urea.