IMMUNOCHEMICAL PROPERTIES OF S-100 PROTEINS AND THEIR SUBUNITS

Abstract— The immunological activities of two populations of bovine S-100 proteins with anti-S-100 serum were studied by complement fixation and rocket immunoelectrophoresis. The reactivities of subunits of these two populations were studied by crossed immunoelectrophoresis and rocket immunoelectrophoresis. Although the two populations conformed in all respects to the properties of S-100 protein, the immunological reactivity of one, III-IVa-1, was significantly lower than that of the other, III-IVb-1. The difference was much larger when the S-100 protein fractions were isolated in the absence of aids (mercaptoethanol, EDTA, EGTA, protease inhibitors). With bovine S-100 fractions, the three subunits separated by differences in charge as well as the four subunits separated by differences in molecular weight all reacted with the same antibody molecules in the antiserum. The reactivities of the subunits showed large quantitative differences.
Two populations of S-100 proteins from rat brain also showed differences in reactivity with anti-S-100 serum. The two subunits in each of these fractions reacted with anti-S-100 serum but with quantitative differences, the larger having almost double the activity of the smaller. These results provide firm evidence for the heterogeneity of S-100 proteins based on immunological activity of their subunit components. Different molecular species of S-100 proteins probably differ considerably in their reactivity with antibodies to S-100 protein. Some of the more reactive molecular species also appear to be much more labile, since the reactivity of some S-100 protein fractions was considerably reduced when they were isolated in the absence of aids.