Phosphoenolpyruvate carboxylase of Thiobacillus thioparus. I. General properties

Phosphoenolpyruvate (PEP) carboxylase (orthophosphate:oxalacetate carboxylase (phosphorylating), EC 4.1.1.31) was purified 19-fold from the obligate chemoautotroph, Thiobacillus thioparus. Michaelis constants for the substrates were found to be 0.44 mM for phosphoenolpyruvate, 0.89 mM for bicarbonate, and 0.37 mM for magnesium, using Tris-HC1, pH 7.3. 1-Aspartate, 1-malate, and orthophosphate were found to be inhibitors of enzyme activity, while acetyl CoA, FDP, GTP, and CDP had no effect. Dioxane greatly stimulated enzyme activity.