Distribution of serpins in the tissues of the tobacco hornworm (Manduca sexta) larvae. Existence of new serpins possibly encoded by a gene distinct from the serpin-1 gene

Polyclonal antibodies were raised against the isolated hemolymph serine proteinase inhibitors (serpins) of Manduca sexta larvae. Two of these antibodies, MsH49a and MsH49b, displayed characteristic differences in labelling patterns of hemocytes, fat body, integumental epidermis and cuticle on immunoblots, and in light- and electronmicroscopic sections. The serpin composition of the latter three tissue homogenates was determined by native immunoblots and inhibitor binding assays. The results were compared to the hemolymph samples containing all the known inhibitors encoded by the well-characterized serpin-1 gene. The enzyme specificity of the MsH49b-labelled cuticular serpin was similar to serpin-1J, although its electrophoretic mobility on native PAGE was not identical with any of the known proteinase inhibitors encoded by the serpin-1 gene. Based on these data, we suggest that the cuticle and hemolymph may contain novel serpin(s) encoded by a gene other than the serpin-1 gene. Since the serpin-1J proved to be involved in the activation pathway of the prophenoloxidase system in the hemolymph, the in vivo function of cuticular MsH49b serpin was investigated by prophenoloxidase tests in native cuticular homogenates. Our results demonstrated that the cuticular serpin(s) that are labelled by the MsH49b antibody may play a determinant role in the regulation of the prophenoloxidase system of the integumental cuticle.