Studies on the surface of chick blastoderm cells. 3. Calcium binding to ionogenic sites

The effect of increasing calcium concentrations on the electrophoretic mobility of cells obtained from early chick blastoderms at successive developmental stages was studied. Cells had zero mobilities at calcium concentrations in the range of 1 to 2 × 10^?2 M CaCl₂, and became positively charged when calcium concentrations between 2 and 5 × 10^?2 M CaCl₂ were used. Results using trypsin suggest that while some calcium binding sites disappear from the surface ionogenic layer, the majority of them are not removed by this enzyme. The calcium binding capacity did not vary appreciably in the stages studied. Charge reversal induced by calcium is reversible.