Carboxysomal Diffusion Resistance to Ribulose 1,5-Bisphosphate and 3- Phosphoglycerate in the Cyanobacterium Synechococcus PCC7942

Two preparations of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBisCO; EC 4.1.2.39) were obtained from the cyanobacterium Synechococcus PCC7942. In one preparation, the majority of RuBisCO was insoluble to be localized in carboxysomes ("Carboxysomal RuBisCO"), whereas in the other, the enzyme was solubilized ("Solubilized RuBisCO"). The kinetic properties of both RuBisCO preparations were determined to elucidate the changes of the activity based on packing the enzyme in carboxysomes. The activity of Carboxysomal RuBisCO decreased with increasing reaction time. The apparent affinity of the Carboxysomal RuBisCO for RuBP was lower than that of the Solubilized RuBisCO. The 3-phosphoglycerate produced in carboxysomes was detected with a lag of three minutes. These results suggest that RuBisCO activity changes dependent on packing in carboxysomes and have a diffusion resistance to RuBP and PGA.