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.

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 degrees C, the bound protein becomes progressively less accessible to the dissociating agents of 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.