Acc. Plette et al., COMPETITIVE-BINDING OF PROTONS, CALCIUM, CADMIUM, AND ZINC TO ISOLATED CELL-WALLS OF A GRAM-POSITIVE SOIL BACTERIUM, Environmental science & technology, 30(6), 1996, pp. 1902-1910
Metal ion binding to the bacterial cell wall is the first step in the
interactions of a metal with a bacterium. Cadmium and zinc ion binding
to isolated cell walls of Rhodococcus erythropolis A177 has been stud
ied for a wide range of proton and calcium concentrations. The release
of calcium ions and protons during metal ion binding is an indication
of the competitive nature of the binding. Calculations, based on the
metal binding data and the pH-dependent charging behavior, reveal that
the cell wall becomes positively charged at high coverage with bivale
nt ions. A cooperative effect of the presence of calcium on metal ion
binding was observed. Apparently, the cell wall structure is altered i
n the presence of bivalent ions. Since calcium is a dominant bivalent
cation in most natural systems, one may regard the calcium as a ''stru
cture determining ion''. On the basis of a qualitative interpretation
of the data, the NICA model was selected for a quantitative descriptio
n of the data.