PHOSPHOENOLPYRUVATE CARBOXYLASE FROM HETEROTROPHICALLY CULTURED CATHARANTHUS-ROSEUS CELLS

Maximum activity of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) was detected at the stationary phase of growth of Catharanthus roseus cells in a heterotrophic culture. The activity of PEPC, after partial purification by fractionation with ammonium sulphate and chromatography on Q-Sepharose, was greatly influenced by pH. The K(m) of phosphoenolpyruvate (PEP) was 23 muM at pH 8.0 and 45 muM at pH 7.4. Malate, aspartate, citrate, ATP, pyrophosphate and Pi acted as inhibitors of PEPC, but the extent of inhibition varied in each case with the pH of the reaction mixture. By contrast, glucose-6-phosphate, fructose-1,6-bisphosphate and acetyl-CoA, known as stimulators of the activity of PEPC from other sources, had little or no effect on the activity of the partially purified PEPC. The possible role and mechanism of regulation of PEPC in C. roseus cells are discussed.