The immunoprotein scolexin and its synthesizing sites - The midgut epithelium and the epidermis

Scolexin is one of the bacterial induced hemolymph proteins of tobacco horn worm (Manduca sexta) larvae, that has hemocyte coagulation-provoking activi ty. The 72 kDa scolexin complex is composed of two 36 kDa subunits. To exam ine the protein secretory pathways in insect epithelia a polyclonal antibod y was raised against the 36 kDa hemolymph protein. This MsH36 antibody reco gnised a 36 and a 72 kDa protein in tissue homogenates. On the basis of the characteristic labelling pattern observed on immunoblots and immunocytoche mical sections we concluded that the 36 kDa protein in the hemolymph, in th e midgut and in the epidermis was identical with the scolexin subunit. In p resent paper we report a labelling shift in the midgut epithelium between g oblet and columnar cells that may be controlled by the hormonal system. A 7 2 kDa protein showed similar epitops and molecular weight to the scolexin c omplex and was detected in epidermis and in cuticle under both reducing and non-reducing conditions. Tissue localization of 36 kDa and 72 kDa MsH36 an tibody labelling proteins indicated the possibility that the epidermal cell s produce two kinds of scolexin-like proteins. The complex composed of 36 k Da subunits are transported basolaterally into the circulation and display hemocyte coagulation inducing activity while the 72 kDa form contains two s ubunits linked covalently secreted apically into the cuticle,