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Tyrosine‐89 is important for enzymatic activity of S. cerevisiae inorganic pyrophosphatase
Author(s) -
Raznikov Andrey V.,
Sklyankina Vera A.,
Avaeva Svetlana M.
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)81051-m
Subject(s) - chemistry , pyrophosphate , pyrophosphatase , enzyme , inorganic pyrophosphatase , stereochemistry , binding site , affinity label , active site , affinity labeling , substrate (aquarium) , trypsin , chymotrypsin , biochemistry , biology , ecology
7‐Chloro‐4‐nitro‐benzofurazan selectively modifies one PPase Tyr residue per subunit and lowers the enzyme activity. Hydrolysis of the modified protein by trypsin and then by chymotrypsin produces the 82–89 peptide which possesses modified Tyr‐89. Substrate analog (CaPP i ) and the product of the enzyme reaction, MgP 1 , protect the enzyme against inactivation. Ions of metal‐activators (Mg 2+ , Zn 2+ ) exert no influence on the inactivation rate. On the contrary, the Ca 2+ ‐inhibitor of the enzyme accelerates the reaction by binding to the high‐affinity site, and effectively decreases it when Ca 2+ binds to both sites. Mg 2+ competes with Ca 2+ for one binding site, which is the low affinity site for Mg 2+ and the high‐affinity site for Ca 2+ . The Ca 2+ saturation of the high‐affinity site decreases the p K 2 of Tyr‐89, probably due to direct coordination between Tyr and Ca 2+ . The observed properties of Tyr‐89 modification enable us to propose that Tyr‐89 serves as a proton donor for phosphate releasing during enzymatic hydrolysis of pyrophosphate. The Ca 2+ inhibitory effect on the enzyme activity may be due to the existence of a Tyr‐89 bond in the Cn 2+ pyrophosphatase complex.