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 roseu s cells in a heterotrophic culture. The activity of PEPC, after partia l purification by fractionation with ammonium sulphate and chromatogra phy on Q-Sepharose, was greatly influenced by pH. The K(m) of phosphoe nolpyruvate (PEP) was 23 muM at pH 8.0 and 45 muM at pH 7.4. Malate, a spartate, citrate, ATP, pyrophosphate and Pi acted as inhibitors of PE PC, but the extent of inhibition varied in each case with the pH of th e reaction mixture. By contrast, glucose-6-phosphate, fructose-1,6-bis phosphate and acetyl-CoA, known as stimulators of the activity of PEPC from other sources, had little or no effect on the activity of the pa rtially purified PEPC. The possible role and mechanism of regulation o f PEPC in C. roseus cells are discussed.