The Specific Interaction of S-100 Protein with Synaptosomal Particulate Fractions. Evidence for the Formation of a Tight Complex Between S-100 and Its Binding Sites

Abstract: The dissociation of the ¹²⁵I-labelled S-100 specifically bound to synaptosomal particulate fractions (SYN) has been studied under a variety of conditions after different association times. The results indicate that after a critical association time of about 20 min at 37°C, the bound protein becomes progressively less accessible to the dissociating agents or conditions employed. These findings support the view that the partial irreversibility of the ¹²⁵I-labelled S-100 binding to SYN could be due to the formation of a tight complex between the protein and its synaptosomal sites. These data are discussed mainly in relation to the particulate-bound fraction of native S-100.