title: The relative hydrolytic reactivities of pyrophosphites and pyrophosphates.
abstract: The pH-rate profiles for the hydrolysis of pyrophosphate (PP(V)) and pyrophosphite (PP(III), pyro-di-H-phosphonate) are a complex function of pH, reflecting the different ionic species and their relative reactivities. PP(III) is more reactive than PP(V) at all pHs and only PP(III) shows a hydroxide-ion reaction at high pH, so it is 10(10)-fold more reactive than PP(V) in 0.1 M NaOH. The pK(a2) of PP(III) ~0.44, so the dominant species at pH's > 1 is the di-anion PP(III)(2-). Although there is no observable (NMR or ITC) binding of Mg(2+) to the PP(III) di-anion there is a modest increase in the rate of hydrolysis of PP(III) by Mg(2+). PP(III) is neither a substrate nor an inhibitor of pyrophosphatase, the enzyme that efficiently catalyses the hydrolysis of PP(V).
authors.affiliation: IPOS, The Page Laboratories, Department of Chemical and Biological Sciences, The University of Huddersfield, Queensgate, Huddersfield, HD1 3DH, UK.
authors.forename: Dharmit
authors.initials: D
authors.lastname: Mistry
authors.forename: Nicholas
authors.initials: N
authors.lastname: Powles
mesh_terms: D002384:Catalysis; D011756:Diphosphates / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D015394:Molecular Structure; D009994:Osmolar Concentration; D017905:Phosphites / Q000737:chemistry*; D011755:Pyrophosphatases / Q000737:chemistry / Q000378:metabolism
chemical_list: D011756:Diphosphates; D017905:Phosphites; D011755:Pyrophosphatases; D008274:Magnesium