title: The formation of enzyme-bound and medium pyrophosphate and the molecular basis of the oxygen exchange reaction of yeast inorganic pyrophosphatase.
abstract: Yeast inorganic pyrophosphatase, with 10 mM 32Pi and 10 mM Mg2+ present at pH 7.3 TO 7.6, rapidly forms enzyme-bound pyrophosphate equivalent to about 5% of the total catalytic sties on the two enzyme subunits. The enzyme thus appears to bind PPi so as to favor thermodynamically its formation from Pi. The enzyme catalyzes a measurable equilibrium formation of free PPi at a much slower rate. Under similar conditions, the enzyme catalyzes a rapid exchange of oxygen atoms between Pi and water with the relative activation by metals being Mg2+ greater than Zn2+ greater than Co2+ greater than Mn2+. Millisecond mixing and quenching experiments demonstrate that the rate of formation and cleavage of the enzyme-bound PPi is rapid enough to explain most or all of the oxygen exchange reaction.
mesh_terms: D002413:Cations, Divalent; D011756:Diphosphates / Q000378:metabolism*; D004789:Enzyme Activation; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010100:Oxygen; D011485:Protein Binding; D011755:Pyrophosphatases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D002413:Cations, Divalent; D011756:Diphosphates; D011755:Pyrophosphatases; D008274:Magnesium; D010100:Oxygen