Iron-binding affinity of bacterial vaccine polysaccharides which contain phosphodiester linkages as part of the polymer chain and of other polyphosphates, including DNA.

Abstract

The interaction of iron (II) with bacterial polysaccharides, possessing phosphodiester bonds as part of their polymer chain, has been studied by equilibrium binding dialysis using atomic absorption spectrophotometry. Ferrous ions were found to bind with a stoichiometry of one per two phosphates and with a binding constant of about 2.5 x 10(3) M-1. Similar results, but with larger (ca 1 x 10(4) M-1) binding constants were observed with DNA. This interaction helps explain the depolymerization of polyphosphates which has been observed in the presence of iron salts, and highlights the need to avoid iron contamination of vaccines (and other substances) which contain phosphodiester bonds. The interaction may also be a means of iron sequestration in bacteria which possess these cell-surface polyphosphates.