COMPETITIVE-BINDING OF CALCIUM AND MAGNESIUM TO STREPTOCOCCAL LIPOTEICHOIC ACID

Equilibrium dialysis was used to investigate the binding-capacity and affinity of lipoteichoic acid (LTA) from the Gram-positive bacterium S treptococcus sanguis for calcium and magnesium by a competitive method . LTA was shown to bind approx. 1 mol of either calcium or magnesium p er mole phosphate. Calcium and magnesium dissociation constants were f ound to be 8.39 +/- 0.31 mmol/l and 15.01 +/- 2.01 mmol/l respectively , indicating that S. sanguis LTA will preferentially bind calcium. LTA may act as a calcium buffer by reducing the free calcium concentratio n to which the cell is exposed. The capacity to produce large quantiti es of LTA could thus be as important as aciduricity in selection of sp ecies at caries-prone sites.