Cd(2+)-induced aggregation of Escherichia coli pyrophosphatase.

We report here that Escherichia coli pyrophosphatase aggregates in the presence of millimolar Cd(2+). This highly cooperative process was specific to both the metal ion and the protein and could be reversed fully by decreasing the Cd(2+) concentration. Aggregation was enhanced by Mg(2+), the natural cofactor of pyrophosphatase, and Mn(2+).

Modulation of dimer stability in yeast pyrophosphatase by mutations at the subunit interface and ligand binding to the active site.

Yeast (Saccharomyces cerevisiae) pyrophosphatase (Y-PPase) is a tight homodimer with two active sites separated in space from the subunit interface. The present study addresses the effects of mutation of four amino acid residues at the subunit interface on dimer stability and catalytic activity. The W52S variant of Y-PPase is monomeric up to an enzyme concentration of 300 microm, whereas R51S, H87T, and W279S variants produce monomer only in dilute solutions at pH > or = 8.