Author: Penner, P. E.; Cohen, L. H.
Description: ATP is a potent inhibitor of the activity of fumarase from yeast and pig heart (Ki = 0.005 mM and 0.03 mM, respectively). There is a sigmoid relation between the inhibition and the ATP concentration provided that Mg2+ is present. The sigmoid relationship is shown to be due simply to the fact that the MgATP complex does not inhibit, so that with increasing ATP concentration, the inhibition is not fully expressed until Mg2+ is titrated by ATP. Since several other enzymes in energy yielding pathways are known to be inhibited by free ATP but not by MgATP, this type of sigmoidal response is probably an important factor in sharpening feedback responses to ATP. The inhibition by ATP is increased at low pH, suggesting that ATPH3- may be a better inhibitor than ATP4-. Moreover, the ability of magnesium to diminish the inhibition is reduced at low pH, as would be expected from the fact that ATPH3- has a lower affinity than ATP4- for Mg2+. These phenomena may profoundly affect the metabolic consequences of intracellular cation movements, i.e. exchange of Mg2+ for H+ between two compartments such as mitochondria and cytosol would result in the liberation of ATP from MgATP in one compartment and binding of ATP in the other, producing inverse metabolic effects in the two compartments.
Subject headings: Acetates; Adenosine Triphosphate; Animals; Chemical Phenomena; Chemistry; Chlorides; Citrates; Edetic Acid; Fumarates; Gluconeogenesis; Hydro-Lyases; Hydrogen-Ion Concentration; Kinetics; Liver; Magnesium; Malates; Myocardium; Nucleotides; Phosphates; Saccharomyces; Spectrophotometry; Sulfates; Swine
Publication year: 1969
Journal or book title: The Journal of Biological Chemistry
Volume: 244
Issue: 3
Pages: 1070-1075
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Serial number: 3843