Identification and Characterization of Sulfhydryl-Containing Proteolytic Fragments Involved in the Ca-Induced Conformational Change of Beef Brain S 100

The Ca++-dependent conformational alteration of the S 100 protein was studied by reacting the protein with N-ethyl [2, 3-14C]maleimide in the absence and presence of Ca++ and under denaturing conditions. Peptic hydrolysates of the labeled protein were analyzed by HPLC. Labeled peptide fractions were characterized by high voltage electrophoresis and thin layer chromatography. A clear distinction could be made between two classes of sulfhydryl-containing fragments: (a) neutral, hydrophobic, and (b) acidic. Ca++ markedly favoured 14C-incorporation into the former components, while the latter were readily available only under denaturing conditions.