Fluorescent histochemical demonstration of cathepsin B in the rat yolk sac

Fluorescence demonstration of cathepsin B (E.C. 3.4.22.1) activity was performed in the yolk sac of rats near term (18th day of gestation). The enzyme demonstration was performed on freeze-dried and celloidin mounted yolk-sac sections using different substituted beta-naphthylamide derivatives as substrates and nitrosalicylaldehyde as coupling agent. The discrete reaction products are localized preferentially in the apical part of the visceral yolk-sac epithelium. There is little doubt that cathepsin B is contained here in the well developed lysosomal apparatus of the yolk-sac epithelium.