Phosphoenolpyruvate carboxykinase from chicken liver mitochondria and rat liver cytosol catalyzes the phosphorylation of α-substituted carboxylic acids such as glycolate, thioglycolate, and DL-β-chlorolactate in reactions with absolute requirements for divalent cation activators. 31P NMR analysis of the reaction products indicates that phosphorylation occurs at the α-position to generate the corresponding O- or S-bridged phosphate monoester. In addition, the enzymes catalyze the bicarbonate-dependent phosphorylation of hydroxylamine. The chicken liver enzyme also catalyzes the bicarbonate-dependent phosphorylation of fluoride ion. The k(cat) values for these substrates are 20-1000-fold slower than the k(cat) for oxaloacetate. Pyruvate and β-hydroxypyruvate are not phosphorylated, since the enzyme does not catalyze the enolization of these compounds. Oxalate, a structural analogue of the enolate of pyruvate, is a competitive inhibitor of phosphoenolpyruvate carboxykinase (K(i) of 5 μM) in the direction of phosphoenolpyruvate formation. Oxalate is also an inhibitor of the chicken liver enzyme in the direction of oxaloacetate formation and in the decarboxylation of oxaloacetate. The chicken liver enzyme is inhibited by β-sulfopyruvate, an isoelectronic analogue of oxaloacetate. The extensive homologies between the reactions catalyzed by phosphoenolpyruvate carboxykinase and pyruvate kinase suggest that the divalent cation activators in these reactions may have similar functions. The substrate specificity indicates that phosphoenolpyruvate carboxykinase decarboxylates oxaloacetate to form the enolate of pyruvate which is then phosphorylated by MgGTP on the enzyme.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - 1990|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology