The regulation of potato phosphoenolpyruvate carboxylase in relation to a metabolic pH-stat.

Phosphoenolpyruvate (PEP) carboxylase (E.C. 4.1.1.31.) was extracted from potato tubers (Solanum tuberosum L.) and investigated for regulatory response to metabolites. The enzyme was found to be activated by sugar phosphates and glycollate and non-competitively inhibited by succinate and fumarate. In both cases the effects were highly dependent on pH, being maximal between pH 7 and 7.6. Rapid extraction techniques demonstrated that the enzyme suffers a sharp decline in activity and sensitivity to metabolites during the first 2 h from extraction. The observed properties of PEP carboxylase were related to the possible role of the enzyme in a metabolic pH-stat.