Regulation of ribulose-bisphosphate carboxylase activity and synthesis in Rhodopseudomonas blastica grown in continuous culture

The growth of Rhodopseudomonas blastica in continuous culture under different limitations show that the organism is metabolically versatile. It responds to changes in the environmental growth conditions which results in large variations in the amount of Ribulose-bisphosphate carboxylase/oxygenase (RuBisCO) synthesized and CO-2 fixed by the whole cells. During growth on malate under aerobic and anaerobic conditions in the chemostat, the synthesis of RuBisCO was repressed. Under these conditions low levels of the Form I and Form II RuBisCO enzymes were synthesized. Under CO-2 limited growth on butyrate, derepression of enzyme synthesis was observed with 80-fold increase in enzyme activity. Under this condition only the Form I enzyme was synthesized. It is concluded from this study that the synthesis of RuBisCO (and perhaps other key enzymes of the Calvin Cycle) in R. blastica is regulated by repression and derepression mechanism which is signalled by CO-2 concentration in the growth medium.