Antibodies against specific membrane proteins of neurosecretory granules isolated from bovine neural lobes.
Membrane proteins from bovine neurosecretory granules isolated by density gradient centrifugation were separated by polyacrylamide gel electrophoresis. A doublet of 120 kDa and and 67 kDa bands were identified as specific proteins of the neurosecretory granule membrane. Antibodies against the 120 kDa doublet were raised in rabbits and characterized by western blotting and immunocytochemistry. Analysis of the antiserum by western blotting showed that this recognizes mainly the 120 kDa doublet and some other minor components which seem to be degradation products. The antiserum against the 120 kDa proteins stained, by immunocytochemistry, specifically the supraoptic and paraventricular neurons of the rat hypothalamo-neurohypophysial system. In the neural lobe the immunoreaction was found around blood vessels on structures which appear to be nerve endings and on Herring bodies. Immunoelectron microscopy using protein A-gold showed that the 120 kDa antigens are located on the membrane of neurosecretory granules in sections of rat neural lobes. The presence of the 120 kDa antigens exclusively in the hypothalamo-neurohypophysial system suggests that these proteins are probably not involved in a general secretory mechanism and that they might be a result of the tissue-specific expression of proteins.