Open AccessTwo pathways of pyrophosphate hydrolysis and synthesis by yeast inorganic pyrophosphatase
Author(s) -
BAYKOV Alexander A.,
SHESTAKOV Alexander S.
Publication year - 1992
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1992.tb16947.x
Subject(s) - pyrophosphate , inorganic pyrophosphatase , chemistry , pyrophosphatase , hydrolysis , catalysis , metal , reaction rate constant , enzyme , yeast , stereochemistry , inorganic chemistry , medicinal chemistry , kinetics , biochemistry , organic chemistry , physics , quantum mechanics
Initial rates of pyrophosphate hydrolysis and synthesis by baker's yeast inorganic pyrophosphatase and equilibrium amounts of enzyme‐bound and free pyrophosphate were measured over wide ranges of Mg 2+ and respective substrate concentrations. Computer analysis of these data, in conjunction with those on phosphate/water oxygen exchange [Kasho, V. N. & Baykov, A. A. (1989) Biochem. Biophys. Res. Comm. 161 , 475–480], yielded values of the equilibrium constants for Mg 2+ binding to free enzyme and central complexes and values of the forward and reverse rate constants for the four reaction steps, namely, PP i binding/release, PP i hydrolysis/synthesis and two P i binding/release steps. All catalytic steps were found to proceed through two parallel pathways, involving 3 or 4 Mg 2+ /PP i or 2 P i bound. Product release is the slowest catalytic event in both hydrolysis and synthesis of pyrophosphate, at least, for the four‐metal pathway. In the hydrolytic reaction, magnesium pyrophosphate binding is faster for the four‐metal pathway, dissociation of the second P i is faster for the three‐metal pathway, while PP i hydrolysis and the release of the first P i may proceed with similar rates. Release of pyrophosphate formed on the enzyme is faster for the three‐metal pathway. Both pathways are expected to operate in vivo , and their relative contributions will vary with changes in the Mg 2+ concentration, thus providing a means for pyrophosphatase‐activity regulation.