[Reaction between calcium and different protein S-100 fractions]

The interaction between various fractions of neurospecific S-100 protein and calcium was studied by means of differential spectrophotometry. Fractions demonstrating "blue" and "red" shifts of the spectrum were detected. The change of conformation, occurring when calcium is bound, results in a redistribution of the protein in the double-phase system (polyetylenglycol-dextran), and the fractions, demonstrating the "blue" shift are transferred to the more hydrophobic phase (PEG), while fractions with the "red" shift move to the less hydrophobic phase (dextran). The existence of fractions with different reaction to calcium binding is discussed considering their participation in controling ionic permeability of neuronal membranes.