Membrane-bound S-100 protein on nerve cells and its distribution.

In this study we present data supporting a heterogeneous distribution of the brain-specific S-100 protein on nerve cell plasma membranes from isolated neurons. This has been shown in a previous study by immunoelectron microscopy using peroxidase-conjugated anti-S-100 antiserum and in this study by immunofluorescence using fluorescein-conjugated anti-S-100 antiserum, the specificity of which is discussed. Incubation of the cells at +23 degrees C or at +4 degrees C did not change the distribution pattern of S-100 over the cell membranes, nor did incubation in antimetabolites, or incubation with univalent Fab fragments. We conclude that the membrane-bound S-100 protein with its heterogeneous and polar distribution on the nerve cells is a sign of a protein differentiation of the neuron.