Human aminopeptidase N carries an apical sorting signal on its ectodomain necessary for its correct transport to the apical membrane in Madin-Darby canine kidney cells. To determine whether the apical sorting signal is localized in the serine/threonine rich stalk or in the catalytic head group, anchor/stalk-minus aminopeptidase N, consisting of the hemagglutinin signal peptide and the catalytic head group of human aminopeptidase N, was expressed in MDCK cells. Anchor/stalk-minus aminopeptidase N was secreted mainly to the apical side. The catalytic head group of human aminopeptidase N thus carries an apical sorting signal.
