Cr(III) complexes as active site probes of yeast inorganic pyrophosphatase

The inert coordination complex of Cr(III) with PP1 (CrPP1) is not a substrate for yeast inorganic pyrophosphatase and does not inhibit the Mg2+-dependent activity of this enzyme. These results, when compared with the effects of CrPP1 on other enzymes and with the effects of other divalent metal ions on this enzyme, suggest that yeast inorganic pyrophosphatase binds substraather than the phosphate groups. Mg2+ partially protects against a slow inactivation of the enzyme by Cr(H2O)6(3)+; this exchange inert ion may provide a means of labeling the metal ion binding site of this enzyme.