title: [Synthesis of pyrophosphate by rat liver cytoplasmic and mitochondrial pyrophosphatases].
abstract: The kinetics of pyrophosphate synthesis catalyzed by rat liver cytosolic and mitochondrial pyrophosphatase in the presence of Mg2+ as cofactor has been studied. According to the kinetic model, this reaction proceeds through two parallel pathways: pathway I utilizing two magnesium phosphate molecules and pathway II utilizing both magnesium phosphate and free phosphate. Pyrophosphate formation is greatly facilitated in the active sites of the enzymes ([E.PPi]/[E.2Pi] = 0.11-0.24). Both enzymes are characterized by high efficiency in pyrophosphate synthesis in solution: the catalytic constants for the cytosolic and mitochondrial pyrophosphatases are 14 and 9.3 s-1, respectively (9 and 16% relative to those for PPi hydrolysis). The results obtained demonstrate that enzyme-catalyzed synthesis of pyrophosphate can proceed at a high rate in the absence of any external energy input, such as that provided by the proton-motive force in membrane systems.
authors.forename: S E
authors.initials: SE
authors.lastname: Volk
authors.forename: A G
authors.initials: AG
authors.lastname: Ivanov
authors.forename: A A
authors.initials: AA
authors.lastname: Baĭkov
mesh_terms: D000818:Animals; D002384:Catalysis; D003593:Cytoplasm / Q000201:enzymology*; D011756:Diphosphates / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology*; D008956:Models, Chemical; D017494:Proton Pumps; D011755:Pyrophosphatases / Q000378:metabolism*; D051381:Rats
chemical_list: D011756:Diphosphates; D017494:Proton Pumps; D011755:Pyrophosphatases
vernacular_title: Sintez pirofosfata tsitoplazmaticheskoĭ i mitokhondrial'noĭ pirofosfatazami pecheni krysy.