Studies during the previous year have shown that the acidic, calcium binding protein which we designate brain TN-C is distinct from the "S-100" protein fraction and is related to rabbit muscle TN-C in physicochemical properties and in amino acid sequence. Brain TN-C has a wide phylogenetic distribution having been detected in and purified from vertebrate brains from mammals to amphibians. Brain TN-C is present in central and peripheral neurosecretory tissue including adrenal medulla where it is present only in the cytosol fraction. Studies for the current year will concentrate on 1) structural studies of brain TN-C; 2) studies of the functional similarities between muscle and brain TN-Cs and 3) studies of the biological function of muscle contractile proteins in neurosecretory tissue using the adrenal medulla as a model system.