PUB - Publikationen an der Universität Bielefeld

FPLC of crude cell extracts of Chlorella kessleri reveals two protein fractions with phosphoenolpyruvate carboxylase activity. Their mole masses, 955 kDa and 543 kDa, suggest that they are dimer and monomer of the same enzyme. Further data, however, indicate that they are more likely two different iso-forms of phosphoenolpyruvate carboxylase: Attempts to interconvert both proteins in vitro, such as through treatment with NaCl, metabolites and thiol- or histidine-group effecting reagents, were unsuccessful. The substrate affinity of the large protein was slightly higher than that of the small protein (K(m) = 1.13 and 0.76 mm, respectively); and the sensitivity to enhanced temperature was more pronounced in the large than in the smaller protein (half lifes = 23 min and 55-60 min, respectively). Some properties of both fractions, however, proved identical: 1. pH optima at pH 8.5-9, 2. Hill coefficients approx. 1, 3. no significant regulatory effect of glutamine, glutamate, aspartate and malate, 4. increase in K(m) and in Hill coefficient by citrate, and 5. identical behaviour in ion exchange chromatography. Functions and localization of the assumed two iso-forms of phosphoenolpyruvate carboxylase remain to be clarified. No specific effects of red or blue light during autotrophic growth on either protein with PEP Co activity could be found.