Calpain activates two transglutaminases from porcine skin.

Two transglutaminases (TGase) with estimated molecular weight of 55,000 (55-K TGase) and 120,000 (120-K TGase) were partially purified from the cytosolic fraction of porcine skin (epidermis-rich preparation) using DEAE-cellulose and gel-filtration chromatographies. The enzyme activities of both transglutaminases were enhanced more than 20-fold by treatment with calpain (Ca2+-dependent cysteine proteinase) in the presence of Ca2+, and this enhancement was inhibited by adding EDTA, leupeptin, or an endogenous calpain-specific inhibitor protein (calpastatin). 55-K TGase was effectively activated by a smaller amount of calpain than was 120-K TGAse, while known activating reagents such as thrombin and dimethyl sulfoxide or heat treatment preferentially activated 120-K TGase. One of the physiological functions of calpain in the epidermis may be the activation of epidermal transglutaminases.