Evolution of carboxylating enzymes involved in paramylon synthesis (phosphoenolpyruvate carboxylase and carboxykinase) in heterotrophically grown Euglena gracilis.

Heterotrophically grown Euglena synthesize grains of paramylon, its reserve carbohydrate, in a vesicular complex of mitochondrial origin. A CO2 fixation activity in dark grown Euglena was demonstrated in the mitochondria via paramylon. At the beginning of the exponential phase of growth, the activity of phosphoenolpyruvate carboxykinase increases before the augmentation of paramylon.At the end of the exponential phase, the activity of this enzyme decreases, and low residual levels persist in the transition and stationary phases of growth. The activity of phosphoenolpyruvate carboxylase evolves inversely during the heterotrophic growth of the algae in succinate- or a lactate-containing medium. A compartmentalized scheme of carbon metabolism in mitochondria is presented.