Fluorescent visualization of binding and internalization of the anticarcinogenic Bowman-Birk type protease inhibitors in transformed fibroblasts.

The Bowman-Birk protease inhibitors from soybeans and chick peas suppress in vitro malignant transformation. This fluorescent microscopy study is designed to visualize the cellular site of action of these protease inhibitors. Binding and internalization of active protease inhibitors occur over a time course of 2 h. The rate and character of fluorescent micrographs obtained are compared to insulin as a positive control. Internalization of both molecules is completely blocked at 4 degrees C. Interpretation of the fluorescent micrographs in conjunction with biochemical data suggests the anticarcinogenic action of Bowman-Birk type protease inhibitors may involve receptor-mediated endocytosis resulting in the internalization of both the protease inhibitors and a membrane-associated protease.