The effect of monovalent ions on polyphosphate binding to Escherichia coliexopolyphosphatase

The thermodynamic driving force for the interaction of Escherichia coli exo polyphosphatase (PPX) with polyphosphate was investigated by varying salt c hoice and concentration. This interaction was found to be cation concentrat ion independent but weakly dependent on the concentration of certain anions . Both of these traits are very uncommon for nonspecific protein-polyelectr olyte interactions. Interpretation of these results based on theory indicat ed that binding was not entropy driven due to release of polyelectrolyte-co ndensed counterions, as is the case for nearly all protein-polyelectrolyte interactions. The thermodynamics of the PPX-polyphosphate interaction showe d similarity only to the interaction of polynucleotides with single strande d binding proteins. (C) 2000 Academic Press.