title: Two pathways for phosphate/water oxygen exchange by yeast inorganic pyrophosphatase.
abstract: A scheme of Mg2+ and Pi binding to yeast inorganic pyrophosphatase has been deduced from the concentration dependencies of the rate of oxygen exchange between Pi and water. The exchange reaction requires the binding of MgPi and free Pi (pathway I) or two MgPi (pathway II) in addition to two Mg2+ ions bound in the absence of Pi. Pathway II predominates above 0.16 mM Mg2+. The rate of formation of bound PPi from bound Pi for pathway II is three times as high as that for pathway I. The results suggest that the binding of the fourth Mg2+ ion to pyrophosphatase stimulates its synthetic vs its hydrolytic capability.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
authors.forename: V N
authors.initials: VN
authors.lastname: Kasho
authors.forename: A A
authors.initials: AA
authors.lastname: Baykov
mesh_terms: D011756:Diphosphates / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D011755:Pyrophosphatases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013816:Thermodynamics; D014867:Water / Q000378:metabolism*
chemical_list: D011756:Diphosphates; D010710:Phosphates; D014867:Water; D011755:Pyrophosphatases; D008274:Magnesium; D010100:Oxygen