MALATE-DEHYDROGENASE FORMS A COMPLEX WITH AND ACTIVATES PHOSPHOENOLPYRUVATE CARBOXYLASE FROM CRASSULACEAN ACID METABOLISM PLANTS

Gel chromatography and kinetic techniques give evidence for the association of malate dehydrogenase (MDH) and phosphoenolpyruvate carboxylase (PEPC) extracted from leaves of the Crassulacean Acid Metabolism plant Kalanchoe blossfeldiana. PEPC and one form of MDH co-eluted in the same peak from Ultrogel AcA 54, Ultrogel AcA 34 or Sephacryl 200. The complex was disrupted by gradient acrylamide gel electrophoresis and reconstituted in vitro by recovering the purified PEPC from the gel in the presence of MDH. This effect of MDH was not obtained with other proteins or enzymes at the same protein concentration. The molecular masses observed for the postulated complex are consistent with the association of one MDH dimer with one PEPC tetrameric form, or under higher ionic strength, one PEPC dimer. The PEPC-MDH interaction was shown to stimulate PEPC activity several times, or to depress it when MDH was in excess, which supports specificity of the effect. The inhibitory action of malate on PEPC activity was affected by the PEPC-MDH association.