Solubilization and Partial Characterization of the S‐100 Protein Binding Activity of Synaptosomal Particulate Fractions1

Chromatographic evidence is presented that 125I‐labelled S‐100 protein binds to the Triton X‐100 extract of synaptosomal membranes obtained from the cerebral cortex of the adult rat. The interaction is specific and saturable with respect to S‐100 concentration. The binding is time‐ and temperature‐dependent. The affinity of the extract for S‐100 is of the same magnitude as that calculated for whole membranes. Treatment of the extract at high temperatures or with trypsin, phospholipase C and neuraminidase reduces the extent of the interaction, while phospholipase D does not affect it. These results further support the view that S‐100 binds to a highly specific site in nervous membranes.