Keratin cross linking and epidermal transglutaminase: a review with observations on the histochemical and immunochemical localization of the enzyme

Abstract

Enzymes known as transglutaminases mediate cross linking of polypeptide chains by ε (γ glutamyl) lysine bonds. Such bonds stabilize structural proteins of many tissues; transglutaminases specific for these tissues have been identified. A calcium and sulfhydryl dependent transglutaminase with a molecular weight of 55,000 has been purified from bovine snout epidermis and used to elicit a specific antiserum to the enzyme. Sites of epidermal transglutaminase activity have been localized in the cytopalsm of upper malpighian and granular cells by two complementary methods. When thin tissue sections were incubated with a fluorescent lysine analog (dansyl cadaverine) and calcium, tissue acceptor sites became fluorescent. Localization was confirmed by fluorescein conjugated antibody labeling of the enzyme in situ. These observations indicate that epidermal transglutaminase cross links epidermal proteins during the final stages of keratinization.