Possible Binding of Epidermolytic Toxin to a Subcellular Fraction of the Epidermis

An in vitro method for assessing the activity of epidermolytic toxin (ET) was developed in this study. It was almost equal in sensitivity to the in vivo assay system in which ET was injected subcutaneously into new‐born mice. By using the in vitro method it was found that ET could induce epidermal splitting after incubation with the skin only for 5 minutes. No epidermolytic activity remained in the reaction mixture. The activity of ET was not abolished by proteinase inhibitors such as Trasylol, ε‐aminocaproic acid or soy bean trypsin inhibitor. It was abolished by an extract from the epidermis of new‐born mice. The inhibitory activity of the extract was preserved by heating at 56°C for 30 minutes. It was destroyed by heating at 80°C for 30 minutes. The activity was found in a subcellular fraction which should contain mitochondria and lysosomes from the epidermal cells. A reduction in the amount of ET was observed in acrylamide gel electrophoresis after incubation of ET with the subcellular fraction. The possible mode of action of ET was discussed.