title: Specific binding of human interferon-gamma to particulates from hemolymph and protocerebrum of tobacco hornworm (Manduca sexta) larvae.
abstract: Specific binding sites for human interferon-gamma (hIFN-gamma) were found on particulates prepared from the hemolymph and protocerebrum of fifth-instar larvae of the tobacco hornworm, Manduca sexta. A portion of these sites could be solubilized in an active form by the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS). A well-defined specific binding was also associated with hemolymph particulate residue after solubilization by CHAPS. About one-half of [125I]hIFN-gamma binding could be displaced by heparin. The bound hIFN-gamma could be covalently cross-linked to the binding sites using disuccinylamide suberate, and the molecular weight range of these complexes was 200-800 kDa as determined by density gradient sedimentation and gel-exclusion chromatography. Only a small fraction of the hemolymph IFN-gamma binding could be competed by another mammalian cytokine, rat prolactin (rPRL), while there was no sensitivity to rat growth hormone. The small specific rPRL binding found in Manduca hemolymph showed an affinity similar to the prolactin sites found in the liver of pregnant rats. The detergent-insoluble Manduca hIFN-gamma binding was bimodal and similar in affinity distribution to the binding found with human platelet membranes (Kdiss range 0.1-2 nM). The detergent-solubilized IFN-gamma sites were homogenous, with a Kdiss of about 1.5 nM. The IFN-gamma binding sites in Manduca tissues may therefore include molecular species similar to the known invertebrate cytokine receptors and proteoglycan co-receptors.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D005260:Female; D013006:Growth Hormone / Q000378:metabolism; D006458:Hemolymph / Q000187:drug effects / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007371:Interferon-gamma / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007814:Larva / Q000378:metabolism; D018402:Manduca / Q000502:physiology*; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D011247:Pregnancy; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014026:Nicotiana / Q000469:parasitology