Variations in ribulose 1,5-bisphosphate carboxylase protein levels, activities and subcellular distribution during photoautotrophic batch culture of Chlorogloeopsis fritschii

Abstract

Ribulose 1,5-bisphosphate (RuBP) carboxylase is present in the cytoplasm and carboxysomes (polyhedral bodies) of the cyanobacterium Chlorogloeopsis fritschii. In vitro enzyme activities have been measured throughout photoautotrophic batch culture, together with RuBP carboxylase protein concentrations, determined by rocket immunoelectrophoresis. Enzyme activities and protein levels in the cytoplasmic and carboxysomal fractions varied in an apparently inverse manner during growth. The RuBP carboxylase activities per unit enzyme protein were maximal in late lag phase/early exponential phase for both cellular enzyme pools. Both rates per unit enzyme protein declined during exponential phase, cytoplasmic enzyme activity remaining consistently higher than that of the carboxysomal enzyme. Activities per unit cytoplasmic and carboxysomal enzyme protein showed very low, similar rates in late stationary phase and death phase. Dialysis experiments indicated that such changes were not due to interference in activity assays by soluble endogenous effectors. Major shifts in the subcellular distribution of RuBP carboxylase protein were found versus culture age, enzyme protein levels being predominantly carboxysomal in lag phase, mainly soluble in exponential phase and then mainly carboxysomal again in stationary/death phase. The data are discussed in terms of carboxysome function and the question of control of RuBP carboxylase synthesis in cyanobacteria.