[Synthesis of pyrophosphate by rat liver cytoplasmic and mitochondrial pyrophosphatases].
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.
Volk
S E
SE
Ivanov
A G
AG
Baĭkov
A A
AA
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
D011756:Diphosphates; D017494:Proton Pumps; D011755:Pyrophosphatases
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