Nucleotide pyrophosphatase from yeast. The presence of bound zinc

Nucleotide pyrophosphatase from yeast was inhibited by thiols, o-phenanthroline, 8-hydroxyquinoline, EDTA, and 8-hydroxyquinoline-5-sulfonic acid. The inhibition by chelating agents was time and concentration dependent. Inhibition by EDTA was decreased by complexing the EDTA with metal ions before addition to the enzyme. The effectiveness of the metal ions in preventing inhibition by EDTA paralleled the stability constants of the EDTA-metal complexes. Partial recovery of EDTA-inhibited enzyme activity was achieved with Zn 2+, Co 2+, Fe 2+, and Mn 2+. Analyses for zinc in the purified enzyme by atomic absorption spectroscopy and by titration with 8-hydroxyquinoline-5-sulfonic acid revealed the presence of approximately 1 g atom/mol of enzyme ( M r 65,000). The data indicate that yeast nucleotide pyrophosphatase is a metalloenzyme in which the zinc plays some role in activity.