Mechanistic implications of the pH independence of inhibition of phosphoglucose isomerase by neutral sugar phosphates.
J Biol Chem, 1975/9/25;250(18):7277-9.
Chirgwin JM, Parsons TF, Noltmann EA
PMID: 240822
Abstract
In contrast to the strongly pH-dependent inhibition of phosphoglucose isomerase by substrate analogues with a free carboxyl group, inhibition of this enzyme by neutral sugar phosphates is essentially invariant between pH 7 and 9. Competitive inhibition constants for glucitol 6-phosphate (40 muM), arabinose 5-phosphate (50 muM), and erythritol 4-phosphate (100 muM) were found to be of the same order of magnitude as that reported previously for substrate binding constants (50 to 240 muM). The unique exception is erythrose 4-phosphate whose Ki (0.7 muM, independent of pH) reflects a tightness of binding similar to that found at pH values near or below neutrality for the transition state analogue 5-phosphorarabinonate. The pH independence of inhibition by erythrose 4-phosphate and other neutral sugar phosphates may reflect a mode and locus of binding to phosphoglucose isomerase different from that of the aldonate inhibitors.
MeSH terms
Animals; Glucose-6-Phosphate Isomerase; Hydrogen-Ion Concentration; Kinetics; Rabbits; Structure-Activity Relationship; Sugar Phosphates
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