Structural relation of two S-100 proteins in bovine brain; subunit composition of S-100a protein.

Dodecyl sulfate/urea/polyacrylamide gel electrophoresis of S-100a protein, one of the two major components of the brain-specific S-100 protein, indicated the presence of two different subunits in the protein. These subunits (alpha and beta subunits) were purified from the aminoethylated protein by column chromatography on Sephadex G-75, and the purified subunits were subjected to analyses. The results have shown that S-100a protein is a dimer of alpha and beta subunits, with each subunit having a molecular weight of approximately 10500. Structural comparison of these subunits with the subunit of S-100b protein, the other component of S-100 protein consisting of two identical subunits with known amino acid sequence, has revealed that the beta subunit and the subunit of S-100b protein are identical, so that S-100a protein is related to S-100b protein by sharing one of the subunits as a common structural constituent.