[Functionally important tyrosine residues in Saccharomyces cerevisiae pyrophosphatase. I. Chemical modification and...

Inorganic pyrophosphatase (PPase) of S. cerevisiae is effectively inactivated by 7-chloro-4-nitrobenzofuran; the CaPP1 substrate analog has a protective effect. The modified enzyme separated from low molecular weight contaminants has an adsorption maximum at 345 nm. Preliminary modification of PPase SH-groups does not influence the enzyme binding to the inhibitor. The PPase activity is reconstituted by beta-mercapto-ethanol; hence, the inhibiting effect of the reagent is due to modification of tyrosine residues. A single reagent-containing peptide was isolated by specific adsorption from the tryptic hydrolysate of modified PPase. Within the primary structure of PPase, this peptide occupies positions 82-111 and contains two tyrosine residues. Hydrolysis of the isolated peptide by chymotrypsin and determination of the structure of fragments obtained by mass spectrometry and automated sequencing revealed that inactivation of PPase is due to selective modification of Tyr89.