Nucleotide regulation of phosphoenolpyruvate carboxylase from Escherichia coli

Adenine, cytosine, guanine, and uracil nucleotides were surveyed as possible modulators of Escherichia coli phosphoenolpyruvate carboxylase. CMP, CDP, CTP, GDP, and GTP activate, ATP and GMP inhibit. The other nucleotides are without effect. Nucleotide activation is synergistic with acetyl-CoA or laurate. Cytosine nucleotide activation is also synergistic with fructose 1,6-diphosphate, whereas guanine nucleotide activation is not. The pH profiles for CMP and GDP activation, studied individually between pH 7.0 and 9.0, are similar to those for activation by fructose 1,6-diphosphate. ATP inhibits activation by acetyl-CoA, laurate, or fructose 1,6-diphosphate. Pairs of activators synergistically relieve the inhibition. Acetyl-CoA with laurate is most effective. Energy charge profiles suggest little sensitivity to charge fluctuation near 0.8. Ribose 5-phosphate also inhibits activation by acetyl-CoA, laurate, or fructose 1,6-diphosphate. GMP selectively inhibits fructose 1,6-diphosphate activation.